dvc: bump to 0.86.2

external_repo: fix bug in path resolution (#3350 )
setup.py: remove gitdb2 dependency and update gitpython
2026-11-03 07:18:26 +01:00 · 2020-02-17 20:30:51 +02:00 · 2020-02-17 20:30:04 +02:00 · 2020-02-17 18:12:30 +02:00 · 2020-02-17 17:54:53 +02:00 · 2020-02-17 17:27:09 +02:00
236 changed files with 6913 additions and 6337 deletions
@@ -5,4 +5,3 @@
 * [ ] ❌ Have you checked DeepSource, CodeClimate, and other sanity checks below? We consider their findings recommendatory and don't expect everything to be addressed. Please review them carefully and fix those that actually improve code or fix bugs.

 Thank you for the contribution - we'll try to review it as soon as possible. 🙏
-
@@ -26,7 +26,7 @@ innosetup/config.ini
 .coverage
 .coverage.*

-*.swp
+*.sw?

 pip-wheel-metadata/
 .vscode/
@@ -1,6 +1,6 @@
 repos:
 -   repo: https://github.com/ambv/black
-    rev: 19.3b0
+    rev: 19.10b0
    hooks:
    - id: black
      language_version: python3
@@ -9,3 +9,9 @@ repos:
    hooks:
    - id: flake8
      language_version: python3
+-   repo: https://github.com/lovesegfault/beautysh
+    rev: master
+    hooks:
+    - id: beautysh
+      language_version: python3
+      args: [-i, '2']  # 2-space indentaion
@@ -1,7 +1,7 @@
 ---
 restylers:
  - name: black
-    image: restyled/restyler-black:v19.3b0
+    image: restyled/restyler-black:v19.10b0
    command:
    - black
    arguments: []
@@ -13,8 +13,6 @@ stages:
  - check
  - test
  - build
-  - name: deploy
-    if: (branch = master OR tag is present) AND repo = iterative/dvc
 # Travis doesn't support testing python on Mac yet, so we need
 # to workaround it by installing it directly with brew.
 #
@@ -35,20 +33,10 @@ jobs:
    install:
    script: ./scripts/ci/check_patch.sh
  # test jobs
-  - name: "2.7 on Windows"
+  - name: "3.7 on Windows"
    stage: test
    os: windows           # Windows 10.0.17134 N/A Build 17134
    language: shell       # 'language: python' is an error on Travis CI Windows
-    env:
-    - PY2=1
-  - name: "3.7 on Windows"
-    os: windows           # Windows 10.0.17134 N/A Build 17134
-    language: shell       # 'language: python' is an error on Travis CI Windows
-  - name: "2.7 on Linux"
-    language: python
-    python: 2.7
-    env:
-    - PY2=1
  - name: "3.5 on Linux"
    language: python
    python: 3.5
@@ -58,14 +46,9 @@ jobs:
  - name: "3.7 on Linux"
    language: python
    python: 3.7
-  - name: "2.7 on Mac"
+  - name: "3.7 on Mac"
    os: osx
-    osx_image: xcode9.4
-    env:
-    - PY2=1
-  - name: "3.6 on Mac"
-    os: osx
-    osx_image: xcode9.4
+    osx_image: xcode11.3
  # build jobs
  - name: "Mac pkg"
    stage: build
@@ -86,51 +69,32 @@ jobs:
    before_install:
    install:
    script: ./scripts/build_posix.sh
-  - name: "Pypi pkgs"
+  - name: "PyPI pkgs"
    language: python
    python: 3.7
    script: ./scripts/build_package.sh
  - name: Snapcraft snap
+    language: python
+    python: 3.7
    addons:
     snaps:
     - name: snapcraft
       channel: stable
       confinement: classic
+     - name: review-tools
+       channel: stable
     - name: lxd
       channel: stable
    env:
    - SNAPCRAFT_IMAGE_INFO: '{"build_url": "$TRAVIS_BUILD_URL"}'
-    before_install:
+    install:
    - sudo /snap/bin/lxd.migrate -yes
    - sudo /snap/bin/lxd waitready
    - sudo /snap/bin/lxd init --auto
-    install:
    script:
-    - sudo snapcraft --use-lxd
+    - ./scripts/build_snap.sh
    after_failure:
    - sudo journalctl -u snapd
-  # deploy jobs
-  - name: "Pypi pkgs"
-    if: tag is present
-    stage: deploy
-    language: python
-    python: 3.7
-    script: ./scripts/build_package.sh
-    deploy:
-    - provider: pypi
-      user:
-        secure: "IOzNfgPoG3ICg3+s4AuZCCnawgd/KqMzeiAB9R0B9Xb6ProPQJp9O3GBZrtg5OJMHdWQQtwULeOh/LWk4sFdXMcX1iNEgm5Tb7DwO7TDtltW14jUgN9AqfY2twj4UIsW/ON8w0P8v36ZoQq1kO6Pfgjijdm3w+9h6rpps8rJ6jXYpVZVO+SSzzijWddanMkEz4GgctZ2r7U5MWlmm1UogF60kEZIZCQykz0yJnhTpP9nMFDKw6Maki/mcfVwTQ/v3RqjzttHei/aaEMGQXYr3TOX8NPYJXerBpjShDZqcgcCfqPzhi7uCwVYaPvRsMMYH5jgtMz/SO3J6ToeGKT0f1F1ihRyCdusg325TMK7Vv8yHJzL4ngeUbb/oqxWtxhLY7f77Lkx6hBwe6ROpTqiQHIfZad5qyIHihKcDcIHo4FwLHVzxR4y+Ds2js5dXwBkUBaEAx0Dmc6ZdgXqxd815GDwv+VVpzXJhtO6qXmKE36F/Oe6eCNG3dk5MdOK4C2DrM9M8MXllqeQtX6JrM2stWlBalAc9Jn4b0xxAoghX3x3G3hNsLc9Uist1VinY2+IcPozusqj66c+Vbi5YngWSbICOjlIcq2GaOlBi3xioGts396442ztf1eLjMVuvykCI3b4Yz/vJYZOZjUvG/6nLfaFQTJLSXkTvI4do3foeY4="
-      password:
-        secure: "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"
-      skip_existing: true
-      file_glob: true
-      file:
-        - dist/dvc*.whl
-        - dist/dvc*.tar.gz
-      skip_cleanup: true
-      on:
-        tags: true
-        repo: iterative/dvc

 before_install:
  - bash ./scripts/ci/before_install.sh
@@ -142,7 +106,6 @@ script:
  - bash ./scripts/ci/script.sh
 deploy:
  - provider: releases
-    condition: "[[ $(./scripts/ci/deploy_condition.sh) == 'true' ]]"
    api_key:
      secure: nyo17gF4Xl6DFL/KVkMewC805Cv+eK99L7SiYCU+WUAYDIzzFL3YJm7fm8bznPeor7DmpO7uSLSveMnJETBtdurW6JWhCTUss4yD66yFzpk6Z5cvHf/1UA5pdMHkkMM54fRaTRt6L2Yal7RPwGEQTBECLXW1Xmf78Y6+0l8lTvXQ9jXOQSRO/63VDKI5Zww2+XytVicUFlr0hLMGKUuaCjjXcQlAPzBgQz3/5Iz6EtzeTf2o+gTPjocbRbSFPikfiBXUn8XlJ8jBj7i114XJRJffw59KxYGDzxp+enfLBULGNoW0Np2hZqkKkPUIdB08C8XVbRXlFYX8cEYBczjqhv8A05p5F5CnltnqQ0KazcoUP2awPVqn68dWNRF+kqrnMBus8euYKIZ4dy/6bVEKJRa84ESJXZVDcwXTAXRqyovSxOlXqg9ZgAImMKBfKn/fpDX2xIvQPaXcnJxKbmcePfdbC1d0HYJ5jkbNaxKE/T15VvhzIho7mJ2WAv1r8QouQUuzqtpzIGbRn/KXHRUzCtyP0k4+eMKMLFOPzg848WsDarP3v8VYiSy4nFY7ZP7DRd3KttvW5bgVbSeO4jPmTgS6TnnpRwual9BJXSG7bjbfpIMii3bNZ7jWL4zpKT9Jfm8w9RGKLcX9HqkZ3+y60+LtYdhEfBvqsIlWQoIJBXg=
    file_glob: true
@@ -151,9 +114,34 @@ deploy:
      - dvc*.deb
      - dvc*.pkg
      - dvc*.exe
-      - dvc*.snap
    skip_cleanup: true
    on:
+      condition: "$(./scripts/ci/deploy_condition.sh dvc*.rpm dvc*.deb dvc*.pkg dvc*.exe)"
      tags: true
      repo: iterative/dvc
      stage: build
+  - provider: pypi
+    user:
+      secure: "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"
+    password:
+      secure: "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"
+    skip_existing: true
+    file_glob: true
+    file:
+      - dist/dvc*.whl
+      - dist/dvc*.tar.gz
+    skip_cleanup: true
+    on:
+      condition: "$(./scripts/ci/deploy_condition.sh dist/dvc*.whl dist/dvc*.tar.gz)"
+      tags: true
+      repo: iterative/dvc
+      stage: build
+  - provider: snap
+    snap: dvc_*.snap
+    channel: $SNAP_CHANNEL
+    skip_cleanup: true
+    on:
+      all_branches: true
+      condition: "$(./scripts/ci/deploy_condition.sh dvc_*.snap) && ($TRAVIS_BRANCH = master || -n $TRAVIS_TAG)"
+      repo: iterative/dvc
+      stage: build
@@ -10,9 +10,13 @@
 • `Tutorial <https://dvc.org/doc/get-started>`_
 • `Mailing List <https://sweedom.us10.list-manage.com/subscribe/post?u=a08bf93caae4063c4e6a351f6&id=24c0ecc49a>`_

-.. image:: https://travis-ci.com/iterative/dvc.svg?branch=master
+.. image:: https://img.shields.io/badge/release-ok-brightgreen
  :target: https://travis-ci.com/iterative/dvc
-  :alt: Travis
+  :alt: Release
+
+.. image:: https://img.shields.io/travis/com/iterative/dvc/master?label=dev
+  :target: https://travis-ci.com/iterative/dvc
+  :alt: Travis dev branch

 .. image:: https://codeclimate.com/github/iterative/dvc/badges/gpa.svg
  :target: https://codeclimate.com/github/iterative/dvc
@@ -153,17 +157,12 @@ Currently, this includes support for Python versions 2.7, 3.6 and 3.7.
 Snap (Snapcraft)
 ----------------

-Download the latest ``dvc_*.snap`` from the
-GitHub `releases page <https://github.com/iterative/dvc/releases>`_.
-
 .. code-block:: bash

-   snap install dvc_*.snap --dangerous --classic
+   snap install dvc --classic

-Once ``dvc`` is released on the snap store
-(`pending request <https://forum.snapcraft.io/t/classic-confinement-request-for-dvc/14124>`_)
-there will be no need to download ``dvc_*.snap`` or use ``--dangerous``
-(``snap install dvc --classic`` would suffice).
+This corresponds to the latest tagged release.
+Add ``--edge`` for the latest ``master`` version.

 Package
 -------
@@ -2,4 +2,4 @@ dvc (0.75.b1) experimental; urgency=low

  * First native Debian package version.

- -- Dmitry Petrov <dmitry@dataversioncontrol.com>  Sat, 07 Dec 2019 09:49:28 +0300
+ -- Dmitry Petrov <dmitry@dvc.org>  Sat, 07 Dec 2019 09:49:28 +0300
@@ -1,5 +1,5 @@
 Source: dvc
-Maintainer: Dmitry Petrov <dmitry@dataversioncontrol.com>
+Maintainer: Dmitry Petrov <dmitry@dvc.org>
 Section: python
 Priority: optional
 Build-Depends: dh-python, python3-setuptools, python3-all, debhelper (>= 9)
@@ -1,10 +1,10 @@
 Format: https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
 Upstream-Name: DVC
-Upstream-Contact: Dmitry Petrov <dmitry@dataversioncontrol.com>
+Upstream-Contact: Dmitry Petrov <dmitry@dvc.org>
 Source: https://github.com/iterative/dvc

 Files: *
-Copyright: Dmitry Petrov <dmitry@dataversioncontrol.com>
+Copyright: Dmitry Petrov <dmitry@dvc.org>
 License: Apache 2.0
 On Debian systems, the full text of the Apache 2.0
 License can be found in the file
@@ -3,8 +3,6 @@ DVC
 ----
 Make your data science projects reproducible and shareable.
 """
-from __future__ import unicode_literals
-
 import warnings

 import dvc.logger
@@ -1,6 +1,4 @@
-"""Main entry point for dvc command line tool."""
-from __future__ import unicode_literals
-
+"""Main entry point for DVC command line tool."""
 import sys

 from dvc.main import main
@@ -16,8 +16,8 @@ from dvc.exceptions import NotDvcRepoError
 from dvc.lock import Lock, LockError
 from dvc.repo import Repo
 from dvc.scm import SCM
-from dvc.utils import env2bool, is_binary, makedirs
-from dvc.utils.compat import str, FileNotFoundError
+from dvc.utils import env2bool, is_binary
+from dvc.utils.fs import makedirs


 logger = logging.getLogger(__name__)
@@ -54,11 +54,8 @@ def is_enabled():
        return False

    enabled = to_bool(
-        Config(validate=False)
-        .config.get(Config.SECTION_CORE, {})
-        .get(Config.SECTION_CORE_ANALYTICS, "true")
+        Config(validate=False).get("core", {}).get("analytics", "true")
    )
-
    logger.debug("Analytics is {}abled.".format("en" if enabled else "dis"))

    return enabled
@@ -76,7 +73,10 @@ def send(report):
    headers = {"content-type": "application/json"}

    with open(report, "rb") as fobj:
-        requests.post(url, data=fobj, headers=headers, timeout=5)
+        try:
+            requests.post(url, data=fobj, headers=headers, timeout=5)
+        except requests.exceptions.RequestException:
+            logger.debug("failed to send analytics report", exc_info=True)

    os.remove(report)

@@ -141,7 +141,7 @@ def _find_or_create_user_id():

    IDs are generated randomly with UUID.
    """
-    config_dir = Config.get_global_config_dir()
+    config_dir = Config.get_dir("global")
    fname = os.path.join(config_dir, "user_id")
    lockfile = os.path.join(config_dir, "user_id.lock")

@@ -1,27 +1,37 @@
 import os
-from contextlib import contextmanager
+from contextlib import contextmanager, _GeneratorContextManager as GCM

-try:
-    from contextlib import _GeneratorContextManager as GCM
-except ImportError:
-    from contextlib import GeneratorContextManager as GCM
-
-from dvc.utils.compat import urlparse
 from dvc.repo import Repo
+from dvc.exceptions import DvcException, NotDvcRepoError
 from dvc.external_repo import external_repo


+class UrlNotDvcRepoError(DvcException):
+    """Thrown if given URL is not a DVC repository.
+
+    Args:
+        url (str): URL to the repository
+    """
+
+    def __init__(self, url):
+        super().__init__("'{}' is not a DVC repository.".format(url))
+
+
 def get_url(path, repo=None, rev=None, remote=None):
-    """Returns an url of a resource specified by path in repo"""
+    """
+    Returns the full URL to the data artifact specified by its `path` in a
+    `repo`.
+    NOTE: There is no guarantee that the file actually exists in that location.
+    """
    with _make_repo(repo, rev=rev) as _repo:
-        abspath = os.path.join(_repo.root_dir, path)
-        out, = _repo.find_outs_by_path(abspath)
+        _require_dvc(_repo)
+        out = _repo.find_out_by_relpath(path)
        remote_obj = _repo.cloud.get_remote(remote)
        return str(remote_obj.checksum_to_path_info(out.checksum))


 def open(path, repo=None, rev=None, remote=None, mode="r", encoding=None):
-    """Opens a specified resource as a file descriptor"""
+    """Context manager to open a file artifact as a file object."""
    args = (path,)
    kwargs = {
        "repo": repo,
@@ -40,21 +50,20 @@ class _OpenContextManager(GCM):

    def __getattr__(self, name):
        raise AttributeError(
-            "dvc.api.open() should be used in a with statement"
+            "dvc.api.open() should be used in a with statement."
        )


 def _open(path, repo=None, rev=None, remote=None, mode="r", encoding=None):
    with _make_repo(repo, rev=rev) as _repo:
-        abspath = os.path.join(_repo.root_dir, path)
-        with _repo.open(
-            abspath, remote=remote, mode=mode, encoding=encoding
+        with _repo.open_by_relpath(
+            path, remote=remote, mode=mode, encoding=encoding
        ) as fd:
            yield fd


 def read(path, repo=None, rev=None, remote=None, mode="r", encoding=None):
-    """Read a specified resource into string"""
+    """Returns the contents of a file artifact."""
    with open(
        path, repo=repo, rev=rev, remote=remote, mode=mode, encoding=encoding
    ) as fd:
@@ -62,10 +71,18 @@ def read(path, repo=None, rev=None, remote=None, mode="r", encoding=None):


@contextmanager
-def _make_repo(repo_url, rev=None):
-    if not repo_url or urlparse(repo_url).scheme == "":
-        assert rev is None, "Custom revision is not supported for local repo"
-        yield Repo(repo_url)
-    else:
-        with external_repo(url=repo_url, rev=rev) as repo:
-            yield repo
+def _make_repo(repo_url=None, rev=None):
+    repo_url = repo_url or os.getcwd()
+    if rev is None and os.path.exists(repo_url):
+        try:
+            yield Repo(repo_url)
+            return
+        except NotDvcRepoError:
+            pass  # fallthrough to external_repo
+    with external_repo(url=repo_url, rev=rev) as repo:
+        yield repo
+
+
+def _require_dvc(repo):
+    if not isinstance(repo, Repo):
+        raise UrlNotDvcRepoError(repo.url)
@@ -1,28 +1,8 @@
-"""Manages cache of a dvc repo."""
-from __future__ import unicode_literals
-
-import os
+"""Manages cache of a DVC repo."""
 from collections import defaultdict

 from funcy import cached_property

-from dvc.config import Config
-from dvc.utils.compat import builtin_str
-
-
-class CacheConfig(object):
-    def __init__(self, config):
-        self.config = config
-
-    def set_dir(self, dname, level=None):
-        from dvc.remote.config import RemoteConfig
-
-        configobj = self.config.get_configobj(level)
-        path = RemoteConfig.resolve_path(dname, configobj.filename)
-        self.config.set(
-            Config.SECTION_CACHE, Config.SECTION_CACHE_DIR, path, level=level
-        )
-

 def _make_remote_property(name):
    """
@@ -56,12 +36,12 @@ def _make_remote_property(name):

        return Remote(self.repo, name=remote)

-    getter.__name__ = builtin_str(name)
+    getter.__name__ = name
    return cached_property(getter)


 class Cache(object):
-    """Class that manages cache locations of a dvc repo.
+    """Class that manages cache locations of a DVC repo.

    Args:
        repo (dvc.repo.Repo): repo instance that this cache belongs to.
@@ -73,37 +53,22 @@ class Cache(object):
        from dvc.remote import Remote

        self.repo = repo
+        self.config = config = repo.config["cache"]

-        self.config = config = repo.config.config[Config.SECTION_CACHE]
-        local = config.get(Config.SECTION_CACHE_LOCAL)
+        local = config.get("local")

        if local:
-            name = Config.SECTION_REMOTE_FMT.format(local)
-            settings = repo.config.config[name]
+            settings = {"name": local}
        else:
-            default_cache_dir = os.path.join(repo.dvc_dir, self.CACHE_DIR)
-            cache_dir = config.get(Config.SECTION_CACHE_DIR, default_cache_dir)
-            cache_type = config.get(Config.SECTION_CACHE_TYPE)
-            protected = config.get(Config.SECTION_CACHE_PROTECTED)
-            shared = config.get(Config.SECTION_CACHE_SHARED)
-
-            settings = {
-                Config.PRIVATE_CWD: config.get(
-                    Config.PRIVATE_CWD, repo.dvc_dir
-                ),
-                Config.SECTION_REMOTE_URL: cache_dir,
-                Config.SECTION_CACHE_TYPE: cache_type,
-                Config.SECTION_CACHE_PROTECTED: protected,
-                Config.SECTION_CACHE_SHARED: shared,
-            }
+            settings = {**config, "url": config["dir"]}

        self.local = Remote(repo, **settings)

-    s3 = _make_remote_property(Config.SECTION_CACHE_S3)
-    gs = _make_remote_property(Config.SECTION_CACHE_GS)
-    ssh = _make_remote_property(Config.SECTION_CACHE_SSH)
-    hdfs = _make_remote_property(Config.SECTION_CACHE_HDFS)
-    azure = _make_remote_property(Config.SECTION_CACHE_AZURE)
+    s3 = _make_remote_property("s3")
+    gs = _make_remote_property("gs")
+    ssh = _make_remote_property("ssh")
+    hdfs = _make_remote_property("hdfs")
+    azure = _make_remote_property("azure")


 class NamedCache(object):
@@ -1,42 +1,42 @@
-"""Command line interface for dvc."""
-from __future__ import print_function
-from __future__ import unicode_literals
-
+"""DVC command line interface"""
 import argparse
 import logging
 import sys

-import dvc.command.add as add
-import dvc.command.cache as cache
-import dvc.command.checkout as checkout
-import dvc.command.commit as commit
-import dvc.command.config as config
-import dvc.command.daemon as daemon
-import dvc.command.data_sync as data_sync
-import dvc.command.destroy as destroy
-import dvc.command.diff as diff
-import dvc.command.gc as gc
-import dvc.command.get as get
-import dvc.command.get_url as get_url
-import dvc.command.imp as imp
-import dvc.command.imp_url as imp_url
-import dvc.command.init as init
-import dvc.command.install as install
-import dvc.command.lock as lock
-import dvc.command.metrics as metrics
-import dvc.command.move as move
-import dvc.command.pipeline as pipeline
-import dvc.command.remote as remote
-import dvc.command.remove as remove
-import dvc.command.repro as repro
-import dvc.command.root as root
-import dvc.command.run as run
-import dvc.command.tag as tag
-import dvc.command.unprotect as unprotect
-import dvc.command.update as update
-import dvc.command.version as version
-from dvc.command.base import fix_subparsers
-from dvc.exceptions import DvcParserError
+from .command import (
+    add,
+    cache,
+    checkout,
+    commit,
+    config,
+    daemon,
+    data_sync,
+    destroy,
+    diff,
+    gc,
+    get,
+    get_url,
+    imp,
+    imp_url,
+    init,
+    install,
+    ls,
+    lock,
+    metrics,
+    move,
+    pipeline,
+    remote,
+    remove,
+    repro,
+    root,
+    run,
+    tag,
+    unprotect,
+    update,
+    version,
+)
+from .command.base import fix_subparsers
+from .exceptions import DvcParserError


 logger = logging.getLogger(__name__)
@@ -63,6 +63,7 @@ COMMANDS = [
    metrics,
    install,
    root,
+    ls,
    lock,
    pipeline,
    daemon,
@@ -92,7 +93,7 @@ class DvcParser(argparse.ArgumentParser):

 class VersionAction(argparse.Action):  # pragma: no cover
    # pylint: disable=too-few-public-methods
-    """Shows dvc version and exits."""
+    """Shows DVC version and exits."""

    def __call__(self, parser, namespace, values, option_string=None):
        from dvc import __version__
@@ -173,7 +174,7 @@ def parse_args(argv=None):
        title="Available Commands",
        metavar="COMMAND",
        dest="cmd",
-        help="Use dvc COMMAND --help for command-specific help.",
+        help="Use `dvc COMMAND --help` for command-specific help.",
    )

    fix_subparsers(subparsers)
@@ -1,13 +1,8 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

-from dvc.command.base import append_doc_link
-from dvc.command.base import CmdBase
-from dvc.exceptions import DvcException
-from dvc.exceptions import RecursiveAddingWhileUsingFilename
-
+from dvc.command.base import append_doc_link, CmdBase
+from dvc.exceptions import DvcException, RecursiveAddingWhileUsingFilename

 logger = logging.getLogger(__name__)

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import logging


@@ -14,11 +12,8 @@ def fix_subparsers(subparsers):
        Args:
            subparsers: subparsers to fix.
    """
-    from dvc.utils.compat import is_py3
-
-    if is_py3:  # pragma: no cover
-        subparsers.required = True
-        subparsers.dest = "cmd"
+    subparsers.required = True
+    subparsers.dest = "cmd"


 def append_doc_link(help_message, path):
@@ -40,7 +35,7 @@ class CmdBase(object):
        self.repo = Repo()
        self.config = self.repo.config
        self.args = args
-        hardlink_lock = self.config.config["core"].get("hardlink_lock", False)
+        hardlink_lock = self.config["core"].get("hardlink_lock", False)
        updater = Updater(self.repo.dvc_dir, hardlink_lock=hardlink_lock)
        updater.check()

@@ -1,20 +1,13 @@
-from __future__ import unicode_literals
-
 import argparse

-from dvc.cache import CacheConfig
-from dvc.command.base import append_doc_link
-from dvc.command.base import fix_subparsers
+from dvc.command.base import append_doc_link, fix_subparsers
 from dvc.command.config import CmdConfig


 class CmdCacheDir(CmdConfig):
-    def __init__(self, args):
-        super(CmdCacheDir, self).__init__(args)
-        self.cache_config = CacheConfig(self.config)
-
    def run(self):
-        self.cache_config.set_dir(self.args.value, level=self.args.level)
+        with self.config.edit(level=self.args.level) as edit:
+            edit["cache"]["dir"] = self.args.value
        return 0


@@ -32,7 +25,8 @@ def add_parser(subparsers, parent_parser):
    )

    cache_subparsers = cache_parser.add_subparsers(
-        dest="cmd", help="Use dvc cache CMD --help for command-specific help."
+        dest="cmd",
+        help="Use `dvc cache CMD --help` for command-specific " "help.",
    )

    fix_subparsers(cache_subparsers)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse

 from dvc.command.base import append_doc_link
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -49,7 +47,7 @@ def add_parser(subparsers, parent_parser):
        "--force",
        action="store_true",
        default=False,
-        help="Commit even if checksums for dependencies/outputs changed.",
+        help="Commit even if hash value for dependencies/outputs changed.",
    )
    commit_parser.add_argument(
        "-d",
@@ -1,36 +1,36 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

-from dvc.command.base import append_doc_link
-from dvc.command.base import CmdBaseNoRepo
-from dvc.config import Config
-
+from dvc.command.base import append_doc_link, CmdBaseNoRepo
+from dvc.config import Config, ConfigError

 logger = logging.getLogger(__name__)


 class CmdConfig(CmdBaseNoRepo):
    def __init__(self, args):
-        super(CmdConfig, self).__init__(args)
+        super().__init__(args)

        self.config = Config(validate=False)

    def run(self):
        section, opt = self.args.name.lower().strip().split(".", 1)

-        if self.args.unset:
-            self.config.unset(section, opt, level=self.args.level)
-        elif self.args.value is None:
-            logger.info(self.config.get(section, opt, level=self.args.level))
-        else:
-            self.config.set(
-                section, opt, self.args.value, level=self.args.level
-            )
+        if self.args.value is None and not self.args.unset:
+            conf = self.config.load_one(self.args.level)
+            self._check(conf, section, opt)
+            logger.info(conf[section][opt])
+            return 0

-        is_write = self.args.unset or self.args.value is not None
-        if is_write and self.args.name == "cache.type":
+        with self.config.edit(self.args.level) as conf:
+            if self.args.unset:
+                self._check(conf, section, opt)
+                del conf[section][opt]
+            else:
+                self._check(conf, section)
+                conf[section][opt] = self.args.value
+
+        if self.args.name == "cache.type":
            logger.warning(
                "You have changed the 'cache.type' option. This doesn't update"
                " any existing workspace file links, but it can be done with:"
@@ -39,30 +39,39 @@ class CmdConfig(CmdBaseNoRepo):

        return 0

+    def _check(self, conf, section, opt=None):
+        if section not in conf:
+            msg = "section {} doesn't exist"
+            raise ConfigError(msg.format(self.args.name))
+
+        if opt and opt not in conf[section]:
+            msg = "option {} doesn't exist"
+            raise ConfigError(msg.format(self.args.name))
+

 parent_config_parser = argparse.ArgumentParser(add_help=False)
 parent_config_parser.add_argument(
    "--global",
    dest="level",
    action="store_const",
-    const=Config.LEVEL_GLOBAL,
+    const="global",
    help="Use global config.",
 )
 parent_config_parser.add_argument(
    "--system",
    dest="level",
    action="store_const",
-    const=Config.LEVEL_SYSTEM,
+    const="system",
    help="Use system config.",
 )
 parent_config_parser.add_argument(
    "--local",
    dest="level",
    action="store_const",
-    const=Config.LEVEL_LOCAL,
+    const="local",
    help="Use local config.",
 )
-parent_config_parser.set_defaults(level=Config.LEVEL_REPO)
+parent_config_parser.set_defaults(level="repo")


 def add_parser(subparsers, parent_parser):
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.command.base import CmdBaseNoRepo
 from dvc.command.base import fix_subparsers

@@ -18,9 +16,7 @@ class CmdDaemonUpdater(CmdDaemonBase):
        root_dir = Repo.find_root()
        dvc_dir = os.path.join(root_dir, Repo.DVC_DIR)
        config = Config(dvc_dir, validate=False)
-        hardlink_lock = config.config.get("core", {}).get(
-            "hardlink_lock", False
-        )
+        hardlink_lock = config.get("core", {}).get("hardlink_lock", False)
        updater = Updater(dvc_dir, hardlink_lock=hardlink_lock)
        updater.fetch(detach=False)

@@ -46,7 +42,8 @@ def add_parser(subparsers, parent_parser):
    )

    daemon_subparsers = daemon_parser.add_subparsers(
-        dest="cmd", help="Use dvc daemon CMD --help for command-specific help."
+        dest="cmd",
+        help="Use `dvc daemon CMD --help` for command-specific " "help.",
    )

    fix_subparsers(daemon_subparsers)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -150,7 +148,8 @@ def add_parser(subparsers, _parent_parser):
    pull_parser.set_defaults(func=CmdDataPull)

    # Push
-    PUSH_HELP = "Push data files to a DVC remote storage."
+    PUSH_HELP = "Uploads files or directories tracked by DVC"
+    " to remote storage."

    push_parser = subparsers.add_parser(
        "push",
@@ -193,7 +192,8 @@ def add_parser(subparsers, _parent_parser):
    push_parser.set_defaults(func=CmdDataPush)

    # Fetch
-    FETCH_HELP = "Fetch data files from a DVC remote storage."
+    FETCH_HELP = "Get files or directories tracked by DVC from remote storage"
+    " into the cache."

    fetch_parser = subparsers.add_parser(
        "fetch",
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,14 +1,11 @@
-from __future__ import unicode_literals
-
 import argparse
+import json
 import logging
+import os

-import humanize
-import inflect
-from funcy import compact
+import colorama

-from dvc.command.base import append_doc_link
-from dvc.command.base import CmdBase
+from dvc.command.base import CmdBase, append_doc_link
 from dvc.exceptions import DvcException


@@ -17,156 +14,144 @@ logger = logging.getLogger(__name__)

 class CmdDiff(CmdBase):
    @staticmethod
-    def _print_size(size):
-        if size < 0:
-            change = "decreased by {}"
-        elif size > 0:
-            change = "increased by {}"
-        else:
-            change = "not changed"
-        natur_size = humanize.naturalsize(abs(size))
-        return change.format(natur_size)
+    def _format(diff):
+        """
+        Given a diff structure, generate a string of paths separated
+        by new lines and grouped together by their state.

-    @staticmethod
-    def _get_md5_string(sign, file_name, checksum):
-        sample_msg = ""
-        if file_name:
-            sample_msg = "{}{} with md5 {}\n"
-            sample_msg = sample_msg.format(sign, file_name, checksum)
-        return sample_msg
+        A group's header is colored and its entries are sorted to enhance
+        readability, for example:

-    @classmethod
-    def _get_dir_changes(cls, dct):
-        import dvc.repo.diff as diff
+            Added:
+                another_file.txt
+                backup.tar
+                dir/
+                dir/1

-        engine = inflect.engine()
-        changes_msg = (
-            "{} {} untouched, {} {} modified, {} {} added, "
-            "{} {} deleted, size was {}"
+        An example of a diff formatted when entries contain checksums:
+
+            Added:
+                d3b07384 foo
+
+            Modified:
+                c157a790..f98bf6f1 bar
+
+        If a group has no entries, it won't be included in the result.
+
+        At the bottom, include a summary with the number of files per state.
+        """
+
+        def _digest(checksum):
+            if type(checksum) is str:
+                return checksum[0:8]
+            return "{}..{}".format(checksum["old"][0:8], checksum["new"][0:8])
+
+        colors = {
+            "added": colorama.Fore.GREEN,
+            "modified": colorama.Fore.YELLOW,
+            "deleted": colorama.Fore.RED,
+        }
+
+        summary = {}
+        groups = []
+
+        for state in ["added", "deleted", "modified"]:
+            summary[state] = 0
+            entries = diff[state]
+
+            if not entries:
+                continue
+
+            content = []
+
+            for entry in entries:
+                path = entry["path"]
+                checksum = entry.get("checksum")
+                summary[state] += 1 if not path.endswith(os.sep) else 0
+                content.append(
+                    "{space}{checksum}{separator}{path}".format(
+                        space="    ",
+                        checksum=_digest(checksum) if checksum else "",
+                        separator="  " if checksum else "",
+                        path=entry["path"],
+                    )
+                )
+
+            groups.append(
+                "{color}{header}{nc}:\n{content}".format(
+                    color=colors[state],
+                    header=state.capitalize(),
+                    nc=colorama.Fore.RESET,
+                    content="\n".join(content),
+                )
+            )
+
+        groups.append(
+            "files summary: {added} added, {deleted} deleted,"
+            " {modified} modified".format_map(summary)
        )
-        changes_msg = changes_msg.format(
-            dct[diff.DIFF_IDENT],
-            engine.plural("file", dct[diff.DIFF_IDENT]),
-            dct[diff.DIFF_CHANGE],
-            engine.plural("file", dct[diff.DIFF_CHANGE]),
-            dct[diff.DIFF_NEW],
-            engine.plural("file", dct[diff.DIFF_NEW]),
-            dct[diff.DIFF_DEL],
-            engine.plural("file", dct[diff.DIFF_DEL]),
-            cls._print_size(dct[diff.DIFF_SIZE]),
-        )
-        return changes_msg

-    @classmethod
-    def _get_file_changes(cls, dct):
-        import dvc.repo.diff as diff
-
-        if (
-            dct.get(diff.DIFF_OLD_FILE)
-            and dct.get(diff.DIFF_NEW_FILE)
-            and dct[diff.DIFF_SIZE] == 0
-        ):
-            msg = "file size was not changed"
-        elif dct.get(diff.DIFF_NEW_FILE):
-            msg = "added file with size {}".format(
-                humanize.naturalsize(dct[diff.DIFF_SIZE])
-            )
-        elif dct.get(diff.DIFF_OLD_FILE):
-            msg = "deleted file with size {}".format(
-                humanize.naturalsize(abs(dct[diff.DIFF_SIZE]))
-            )
-        else:
-            msg = "file was modified, file size {}".format(
-                cls._print_size(dct[diff.DIFF_SIZE])
-            )
-        return msg
-
-    @classmethod
-    def _get_royal_changes(cls, dct):
-        import dvc.repo.diff as diff
-
-        if dct[diff.DIFF_SIZE] != diff.DIFF_SIZE_UNKNOWN:
-            if dct.get("is_dir"):
-                return cls._get_dir_changes(dct)
-            else:
-                return cls._get_file_changes(dct)
-        return "size is ?"
-
-    @classmethod
-    def _show(cls, diff_dct):
-        import dvc.repo.diff as diff
-
-        msg = "dvc diff from {} to {}".format(
-            diff_dct[diff.DIFF_A_REF], diff_dct[diff.DIFF_B_REF]
-        )
-        if diff_dct.get(diff.DIFF_EQUAL):
-            logger.info(msg)
-            return
-        for dct in diff_dct[diff.DIFF_LIST]:
-            msg += "\n\ndiff for '{}'\n".format(dct[diff.DIFF_TARGET])
-            msg += cls._get_md5_string(
-                "-",
-                dct.get(diff.DIFF_OLD_FILE),
-                dct.get(diff.DIFF_OLD_CHECKSUM),
-            )
-            msg += cls._get_md5_string(
-                "+",
-                dct.get(diff.DIFF_NEW_FILE),
-                dct.get(diff.DIFF_NEW_CHECKSUM),
-            )
-            msg += "\n"
-            msg += cls._get_royal_changes(dct)
-        logger.info(msg)
-        return msg
+        return "\n\n".join(groups)

    def run(self):
        try:
-            msg = self.repo.diff(
-                self.args.a_ref, target=self.args.target, b_ref=self.args.b_ref
-            )
-            self._show(msg)
+            diff = self.repo.diff(self.args.a_rev, self.args.b_rev)
+
+            if not any(diff.values()):
+                return 0
+
+            if not self.args.checksums:
+                for _, entries in diff.items():
+                    for entry in entries:
+                        del entry["checksum"]
+
+            if self.args.show_json:
+                res = json.dumps(diff)
+            else:
+                res = self._format(diff)
+
+            logger.info(res)
+
        except DvcException:
-            msg = "failed to get 'diff {}'"
-            args = " ".join(
-                compact([self.args.target, self.args.a_ref, self.args.b_ref])
-            )
-            msg = msg.format(args)
-            logger.exception(msg)
+            logger.exception("failed to get diff")
            return 1
        return 0


 def add_parser(subparsers, parent_parser):
    DIFF_DESCRIPTION = (
-        "Show diff of a data file or a directory that is under DVC control.\n"
-        "Some basic statistics summary, how many files were deleted/changed."
+        "Show changes between commits in the DVC repository,"
+        " or between a commit and the workspace."
+        "Prints the list of paths added, modified, or deleted."
    )
-    DIFF_HELP = "Show a diff of a DVC controlled data file or a directory."
    diff_parser = subparsers.add_parser(
        "diff",
        parents=[parent_parser],
        description=append_doc_link(DIFF_DESCRIPTION, "diff"),
-        help=DIFF_HELP,
+        help=DIFF_DESCRIPTION,
        formatter_class=argparse.RawDescriptionHelpFormatter,
    )
    diff_parser.add_argument(
-        "-t",
-        "--target",
-        help=(
-            "Source path to a data file or directory. Default None. "
-            "If not specified, compares all files and directories "
-            "that are under DVC control in the current working space."
-        ),
+        "a_rev",
+        help="Old Git commit to compare (defaults to HEAD)",
+        nargs="?",
+        default="HEAD",
    )
    diff_parser.add_argument(
-        "a_ref", help="Git reference from which diff calculates"
-    )
-    diff_parser.add_argument(
-        "b_ref",
-        help=(
-            "Git reference until which diff calculates, if omitted "
-            "diff shows the difference between current HEAD and a_ref"
-        ),
+        "b_rev",
+        help=("New Git commit to compare (defaults to the current workspace)"),
        nargs="?",
    )
+    diff_parser.add_argument(
+        "--show-json",
+        help="Format the output into a JSON",
+        action="store_true",
+        default=False,
+    )
+    diff_parser.add_argument(
+        "--checksums",
+        help="Display hash value for each entry",
+        action="store_true",
+        default=False,
+    )
    diff_parser.set_defaults(func=CmdDiff)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging
 import os
@@ -54,10 +52,10 @@ class CmdGC(CmdBase):


 def add_parser(subparsers, parent_parser):
-    GC_HELP = "Collect unused data from DVC cache or a remote storage."
+    GC_HELP = "Garbage collect unused objects from cache or remote storage."
    GC_DESCRIPTION = (
-        "Deletes all files in the cache or a remote which are not in\n"
-        "use by the specified git references (defaults to just HEAD)."
+        "Removes all files in the cache or a remote which are not in\n"
+        "use by the specified Git revisions (defaults to just HEAD)."
    )
    gc_parser = subparsers.add_parser(
        "gc",
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -12,7 +10,27 @@ logger = logging.getLogger(__name__)


 class CmdGet(CmdBaseNoRepo):
+    def _show_url(self):
+        from dvc.api import get_url
+
+        try:
+            url = get_url(
+                self.args.path, repo=self.args.url, rev=self.args.rev
+            )
+            logger.info(url)
+        except DvcException:
+            logger.exception("failed to show URL")
+            return 1
+
+        return 0
+
    def run(self):
+        if self.args.show_url:
+            return self._show_url()
+
+        return self._get_file_from_repo()
+
+    def _get_file_from_repo(self):
        from dvc.repo import Repo

        try:
@@ -33,7 +51,7 @@ class CmdGet(CmdBaseNoRepo):


 def add_parser(subparsers, parent_parser):
-    GET_HELP = "Download/copy files or directories from DVC repository."
+    GET_HELP = "Download file or directory tracked by DVC or by Git."
    get_parser = subparsers.add_parser(
        "get",
        parents=[parent_parser],
@@ -42,18 +60,21 @@ def add_parser(subparsers, parent_parser):
        formatter_class=argparse.RawDescriptionHelpFormatter,
    )
    get_parser.add_argument(
-        "url", help="URL of Git repository with DVC project to download from."
+        "url", help="Location of DVC or Git repository to download from"
    )
    get_parser.add_argument(
-        "path", help="Path to a file or directory within a DVC repository."
+        "path", help="Path to a file or directory within the repository"
    )
    get_parser.add_argument(
-        "-o",
-        "--out",
-        nargs="?",
-        help="Destination path to copy/download files to.",
+        "-o", "--out", nargs="?", help="Destination path to download files to"
    )
    get_parser.add_argument(
-        "--rev", nargs="?", help="DVC repository git revision."
+        "--rev", nargs="?", help="Git revision (e.g. SHA, branch, tag)"
+    )
+    get_parser.add_argument(
+        "--show-url",
+        action="store_true",
+        help="Print the storage location (URL) the target data would be "
+        "downloaded from, and exit.",
    )
    get_parser.set_defaults(func=CmdGet)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -32,7 +30,8 @@ class CmdImport(CmdBase):

 def add_parser(subparsers, parent_parser):
    IMPORT_HELP = (
-        "Download data from DVC repository and take it under DVC control."
+        "Download file or directory tracked by DVC or by Git "
+        "into the workspace, and track it."
    )

    import_parser = subparsers.add_parser(
@@ -43,15 +42,15 @@ def add_parser(subparsers, parent_parser):
        formatter_class=argparse.RawTextHelpFormatter,
    )
    import_parser.add_argument(
-        "url", help="URL of Git repository with DVC project to download from."
+        "url", help="Location of DVC or Git repository to download from"
    )
    import_parser.add_argument(
-        "path", help="Path to data within DVC repository."
+        "path", help="Path to a file or directory within the repository"
    )
    import_parser.add_argument(
-        "-o", "--out", nargs="?", help="Destination path to put data to."
+        "-o", "--out", nargs="?", help="Destination path to download files to"
    )
    import_parser.add_argument(
-        "--rev", nargs="?", help="DVC repository git revision."
+        "--rev", nargs="?", help="Git revision (e.g. SHA, branch, tag)"
    )
    import_parser.set_defaults(func=CmdImport)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -21,7 +19,7 @@ class CmdInit(CmdBaseNoRepo):
            )
            self.config = self.repo.config
        except InitError:
-            logger.exception("failed to initiate dvc")
+            logger.exception("failed to initiate DVC")
            return 1
        return 0

@@ -45,7 +43,7 @@ def add_parser(subparsers, parent_parser):
        "--no-scm",
        action="store_true",
        default=False,
-        help="Initiate dvc in directory that is "
+        help="Initiate DVC in directory that is "
        "not tracked by any scm tool (e.g. git).",
    )
    init_parser.add_argument(
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -15,7 +13,7 @@ class CmdInstall(CmdBase):
        try:
            self.repo.install()
        except Exception:
-            logger.exception("failed to install dvc hooks")
+            logger.exception("failed to install DVC Git hooks")
            return 1
        return 0

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -0,0 +1,68 @@
+import argparse
+import logging
+
+from dvc.command.base import append_doc_link
+from dvc.command.base import CmdBaseNoRepo
+from dvc.exceptions import DvcException
+
+
+logger = logging.getLogger(__name__)
+
+
+class CmdList(CmdBaseNoRepo):
+    def run(self):
+        from dvc.repo import Repo
+
+        try:
+            nodes = Repo.ls(
+                self.args.url,
+                self.args.target,
+                rev=self.args.rev,
+                recursive=self.args.recursive,
+                outs_only=self.args.outs_only,
+            )
+            if nodes:
+                logger.info("\n".join(nodes))
+            return 0
+        except DvcException:
+            logger.exception("failed to list '{}'".format(self.args.url))
+            return 1
+
+
+def add_parser(subparsers, parent_parser):
+    LIST_HELP = "List files and DVC outputs in the repo."
+    list_parser = subparsers.add_parser(
+        "list",
+        parents=[parent_parser],
+        description=append_doc_link(LIST_HELP, "list"),
+        help=LIST_HELP,
+        formatter_class=argparse.RawTextHelpFormatter,
+    )
+    list_parser.add_argument(
+        "url",
+        help="Supported urls:\n"
+        "/path/to/file\n"
+        "/path/to/directory\n"
+        "C:\\\\path\\to\\file\n"
+        "C:\\\\path\\to\\directory\n"
+        "https://github.com/path/to/repo\n"
+        "[email protected]:path/to/repo.git\n",
+    )
+    list_parser.add_argument(
+        "-R",
+        "--recursive",
+        action="store_true",
+        help="Recursively list files.",
+    )
+    list_parser.add_argument(
+        "--outs-only", action="store_true", help="Show only DVC outputs."
+    )
+    list_parser.add_argument(
+        "--rev", nargs="?", help="Git revision (e.g. branch, tag, SHA)"
+    )
+    list_parser.add_argument(
+        "target",
+        nargs="?",
+        help="Path to directory within the repository to list outputs for",
+    )
+    list_parser.set_defaults(func=CmdList)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -28,7 +26,12 @@ def show_metrics(metrics, all_branches=False, all_tags=False):
            logger.info("{branch}:".format(branch=branch))

        for fname, metric in val.items():
-            lines = metric if type(metric) is list else metric.splitlines()
+            if isinstance(metric, dict):
+                lines = list(metric.values())
+            elif isinstance(metric, list):
+                lines = metric
+            else:
+                lines = metric.splitlines()

            if len(lines) > 1:
                logger.info("\t{fname}:".format(fname=fname))
@@ -102,6 +105,59 @@ class CmdMetricsRemove(CmdBase):
        return 0


+def _show_diff(diff):
+    from texttable import Texttable
+
+    if not diff:
+        return "No changes."
+
+    table = Texttable()
+
+    # remove borders to make it easier for users to copy stuff
+    table.set_chars(("", "", "", ""))
+    table.set_deco(0)
+
+    rows = [["Path", "Metric", "Value", "Change"]]
+    for fname, mdiff in diff.items():
+        for metric, change in mdiff.items():
+            rows.append(
+                [
+                    fname,
+                    metric,
+                    change["new"],
+                    change.get("diff", "diff not supported"),
+                ]
+            )
+    table.add_rows(rows)
+    return table.draw()
+
+
+class CmdMetricsDiff(CmdBase):
+    def run(self):
+        try:
+            diff = self.repo.metrics.diff(
+                a_rev=self.args.a_rev,
+                b_rev=self.args.b_rev,
+                targets=self.args.targets,
+                typ=self.args.type,
+                xpath=self.args.xpath,
+                recursive=self.args.recursive,
+            )
+
+            if self.args.show_json:
+                import json
+
+                logger.info(json.dumps(diff))
+            else:
+                logger.info(_show_diff(diff))
+
+        except DvcException:
+            logger.exception("failed to show metrics diff")
+            return 1
+
+        return 0
+
+
 def add_parser(subparsers, parent_parser):
    METRICS_HELP = "Commands to add, manage, collect and display metrics."

@@ -115,7 +171,7 @@ def add_parser(subparsers, parent_parser):

    metrics_subparsers = metrics_parser.add_subparsers(
        dest="cmd",
-        help="Use dvc metrics CMD --help to display command-specific help.",
+        help="Use `dvc metrics CMD --help` to display command-specific help.",
    )

    fix_subparsers(metrics_subparsers)
@@ -216,3 +272,58 @@ def add_parser(subparsers, parent_parser):
    )
    metrics_remove_parser.add_argument("path", help="Path to a metric file.")
    metrics_remove_parser.set_defaults(func=CmdMetricsRemove)
+
+    METRICS_DIFF_HELP = "Show changes in metrics between commits"
+    " in the DVC repository, or between a commit and the workspace."
+    metrics_diff_parser = metrics_subparsers.add_parser(
+        "diff",
+        parents=[parent_parser],
+        description=append_doc_link(METRICS_DIFF_HELP, "metrics/diff"),
+        help=METRICS_DIFF_HELP,
+        formatter_class=argparse.RawDescriptionHelpFormatter,
+    )
+    metrics_diff_parser.add_argument(
+        "a_rev", nargs="?", help="Old Git commit to compare (defaults to HEAD)"
+    )
+    metrics_diff_parser.add_argument(
+        "b_rev",
+        nargs="?",
+        help=("New Git commit to compare (defaults to the current workspace)"),
+    )
+    metrics_diff_parser.add_argument(
+        "--targets",
+        nargs="*",
+        help=(
+            "Metric files or directories (see -R) to show diff for. "
+            "Shows diff for all metric files by default."
+        ),
+    )
+    metrics_diff_parser.add_argument(
+        "-t",
+        "--type",
+        help=(
+            "Type of metrics (json/tsv/htsv/csv/hcsv). "
+            "It can be detected by the file extension automatically. "
+            "Unsupported types will be treated as raw."
+        ),
+    )
+    metrics_diff_parser.add_argument(
+        "-x", "--xpath", help="json/tsv/htsv/csv/hcsv path."
+    )
+    metrics_diff_parser.add_argument(
+        "-R",
+        "--recursive",
+        action="store_true",
+        default=False,
+        help=(
+            "If any target is a directory, recursively search and process "
+            "metric files."
+        ),
+    )
+    metrics_diff_parser.add_argument(
+        "--show-json",
+        action="store_true",
+        default=False,
+        help="Show output in JSON format.",
+    )
+    metrics_diff_parser.set_defaults(func=CmdMetricsDiff)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,14 +1,8 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

-from dvc.command.base import append_doc_link
-from dvc.command.base import CmdBase
-from dvc.command.base import fix_subparsers
+from dvc.command.base import CmdBase, append_doc_link, fix_subparsers
 from dvc.exceptions import DvcException
-from dvc.utils import relpath
-from dvc.utils.compat import str


 logger = logging.getLogger(__name__)
@@ -21,69 +15,66 @@ class CmdPipelineShow(CmdBase):

        stage = Stage.load(self.repo, target)
        G = self.repo.graph
-        stages = networkx.get_node_attributes(G, "stage")
-        node = relpath(stage.path, self.repo.root_dir)
-        nodes = networkx.dfs_postorder_nodes(G, node)
+        stages = networkx.dfs_postorder_nodes(G, stage)

        if locked:
-            nodes = [n for n in nodes if stages[n].locked]
+            stages = [s for s in stages if s.locked]

-        for n in nodes:
+        for stage in stages:
            if commands:
-                if stages[n].cmd is None:
+                if stage.cmd is None:
                    continue
-                logger.info(stages[n].cmd)
+                logger.info(stage.cmd)
            elif outs:
-                for out in stages[n].outs:
+                for out in stage.outs:
                    logger.info(str(out))
            else:
-                logger.info(n)
+                logger.info(stage.path_in_repo)

-    def __build_graph(self, target, commands, outs):
+    def _build_graph(self, target, commands, outs):
        import networkx
        from dvc.stage import Stage
        from dvc.repo.graph import get_pipeline

-        stage = Stage.load(self.repo, target)
-        node = relpath(stage.path, self.repo.root_dir)
+        target_stage = Stage.load(self.repo, target)
+        G = get_pipeline(self.repo.pipelines, target_stage)

-        G = get_pipeline(self.repo.pipelines, node)
-        stages = networkx.get_node_attributes(G, "stage")
-
-        nodes = []
-        for n in G:
-            stage = stages[n]
+        nodes = set()
+        for stage in networkx.dfs_preorder_nodes(G, target_stage):
            if commands:
                if stage.cmd is None:
                    continue
-                nodes.append(stage.cmd)
+                nodes.add(stage.cmd)
            elif outs:
                for out in stage.outs:
-                    nodes.append(str(out))
+                    nodes.add(str(out))
+                for dep in stage.deps:
+                    nodes.add(str(dep))
            else:
-                nodes.append(stage.relpath)
+                nodes.add(stage.relpath)

        edges = []
-        for e in G.edges():
-            from_stage = stages[e[0]]
-            to_stage = stages[e[1]]
-            if commands:
-                if to_stage.cmd is None:
-                    continue
-                edges.append((from_stage.cmd, to_stage.cmd))
-            elif outs:
-                for from_out in from_stage.outs:
-                    for to_out in to_stage.outs:
-                        edges.append((str(from_out), str(to_out)))
-            else:
-                edges.append((from_stage.relpath, to_stage.relpath))

-        return nodes, edges, networkx.is_tree(G)
+        if outs:
+            for stage in networkx.dfs_preorder_nodes(G, target_stage):
+                for dep in stage.deps:
+                    for out in stage.outs:
+                        edges.append((str(out), str(dep)))
+        else:
+            for from_stage, to_stage in networkx.dfs_edges(G, target_stage):
+                if commands:
+                    if to_stage.cmd is None:
+                        continue
+                    edges.append((from_stage.cmd, to_stage.cmd))
+                else:
+                    edges.append((from_stage.relpath, to_stage.relpath))
+
+        return list(nodes), edges, networkx.is_tree(G)

    def _show_ascii(self, target, commands, outs):
        from dvc.dagascii import draw

-        nodes, edges, _ = self.__build_graph(target, commands, outs)
+        nodes, edges, _ = self._build_graph(target, commands, outs)

        if not nodes:
            return
@@ -93,7 +84,7 @@ class CmdPipelineShow(CmdBase):
    def _show_dependencies_tree(self, target, commands, outs):
        from treelib import Tree

-        nodes, edges, is_tree = self.__build_graph(target, commands, outs)
+        nodes, edges, is_tree = self._build_graph(target, commands, outs)
        if not nodes:
            return
        if not is_tree:
@@ -114,18 +105,18 @@ class CmdPipelineShow(CmdBase):
            observe_list.pop(0)
        tree.show()

-    def __write_dot(self, target, commands, outs):
-        from dvc.utils.compat import StringIO
+    def _write_dot(self, target, commands, outs):
+        import io
        import networkx
        from networkx.drawing.nx_pydot import write_dot

-        _, edges, _ = self.__build_graph(target, commands, outs)
+        _, edges, _ = self._build_graph(target, commands, outs)
        edges = [edge[::-1] for edge in edges]

        simple_g = networkx.DiGraph()
        simple_g.add_edges_from(edges)

-        dot_file = StringIO()
+        dot_file = io.StringIO()
        write_dot(simple_g, dot_file)
        logger.info(dot_file.getvalue())

@@ -140,9 +131,7 @@ class CmdPipelineShow(CmdBase):
                        target, self.args.commands, self.args.outs
                    )
                elif self.args.dot:
-                    self.__write_dot(
-                        target, self.args.commands, self.args.outs
-                    )
+                    self._write_dot(target, self.args.commands, self.args.outs)
                elif self.args.tree:
                    self._show_dependencies_tree(
                        target, self.args.commands, self.args.outs
@@ -163,14 +152,11 @@ class CmdPipelineShow(CmdBase):

 class CmdPipelineList(CmdBase):
    def run(self):
-        import networkx
-
        pipelines = self.repo.pipelines
-        for p in pipelines:
-            stages = networkx.get_node_attributes(p, "stage")
-            for stage in stages:
-                logger.info(stage)
-            if len(stages) != 0:
+        for pipeline in pipelines:
+            for stage in pipeline:
+                logger.info(stage.relpath)
+            if len(pipeline) != 0:
                logger.info("=" * 80)
        logger.info("{} pipelines total".format(len(pipelines)))

@@ -189,7 +175,7 @@ def add_parser(subparsers, parent_parser):

    pipeline_subparsers = pipeline_parser.add_subparsers(
        dest="cmd",
-        help="Use dvc pipeline CMD --help for command-specific help.",
+        help="Use `dvc pipeline CMD --help` for command-specific help.",
    )

    fix_subparsers(pipeline_subparsers)
@@ -1,73 +1,99 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

-from dvc.command.base import append_doc_link
-from dvc.command.base import fix_subparsers
+from dvc.config import ConfigError
+from dvc.command.base import append_doc_link, fix_subparsers
 from dvc.command.config import CmdConfig
-from dvc.remote.config import RemoteConfig
+from dvc.utils import format_link

 logger = logging.getLogger(__name__)


-class CmdRemoteConfig(CmdConfig):
+class CmdRemote(CmdConfig):
    def __init__(self, args):
-        super(CmdRemoteConfig, self).__init__(args)
-        self.remote_config = RemoteConfig(self.config)
+        super().__init__(args)
+
+        if getattr(self.args, "name", None):
+            self.args.name = self.args.name.lower()
+
+    def _check_exists(self, conf):
+        if self.args.name not in conf["remote"]:
+            raise ConfigError(
+                "remote '{}' doesn't exists.".format(self.args.name)
+            )


-class CmdRemoteAdd(CmdRemoteConfig):
+class CmdRemoteAdd(CmdRemote):
    def run(self):
        if self.args.default:
            logger.info(
                "Setting '{}' as a default remote.".format(self.args.name)
            )
-        self.remote_config.add(
-            self.args.name,
-            self.args.url,
-            force=self.args.force,
-            default=self.args.default,
-            level=self.args.level,
-        )
+
+        with self.config.edit(self.args.level) as conf:
+            if self.args.name in conf["remote"] and not self.args.force:
+                raise ConfigError(
+                    "remote '{}' already exists. Use `-f|--force` to "
+                    "overwrite it.".format(self.args.name)
+                )
+
+            conf["remote"][self.args.name] = {"url": self.args.url}
+            if self.args.default:
+                conf["core"]["remote"] = self.args.name
+
        return 0


-class CmdRemoteRemove(CmdRemoteConfig):
+class CmdRemoteRemove(CmdRemote):
    def run(self):
-        self.remote_config.remove(self.args.name, level=self.args.level)
+        with self.config.edit(self.args.level) as conf:
+            self._check_exists(conf)
+            del conf["remote"][self.args.name]
+
+        # Remove core.remote refs to this remote in any shadowing configs
+        for level in reversed(self.config.LEVELS):
+            with self.config.edit(level) as conf:
+                if conf["core"].get("remote") == self.args.name:
+                    del conf["core"]["remote"]
+
+            if level == self.args.level:
+                break
+
        return 0


-class CmdRemoteModify(CmdRemoteConfig):
+class CmdRemoteModify(CmdRemote):
    def run(self):
-        self.remote_config.modify(
-            self.args.name,
-            self.args.option,
-            self.args.value,
-            level=self.args.level,
-        )
+        with self.config.edit(self.args.level) as conf:
+            self._check_exists(conf)
+            conf["remote"][self.args.name][self.args.option] = self.args.value
        return 0


-class CmdRemoteDefault(CmdRemoteConfig):
+class CmdRemoteDefault(CmdRemote):
    def run(self):
+
        if self.args.name is None and not self.args.unset:
-            name = self.remote_config.get_default(level=self.args.level)
-            print(name)
+            conf = self.config.load_one(self.args.level)
+            try:
+                print(conf["core"]["remote"])
+            except KeyError:
+                logger.info("No default remote set")
+                return 1
        else:
-            self.remote_config.set_default(
-                self.args.name, unset=self.args.unset, level=self.args.level
-            )
+            with self.config.edit(self.args.level) as conf:
+                if self.args.unset:
+                    conf["core"].pop("remote", None)
+                else:
+                    conf["core"]["remote"] = self.args.name
        return 0


-class CmdRemoteList(CmdRemoteConfig):
+class CmdRemoteList(CmdRemote):
    def run(self):
-        for name, url in self.remote_config.list(
-            level=self.args.level
-        ).items():
-            logger.info("{}\t{}".format(name, url))
+        conf = self.config.load_one(self.args.level)
+        for name, conf in conf["remote"].items():
+            logger.info("{}\t{}".format(name, conf["url"]))
        return 0


@@ -85,7 +111,7 @@ def add_parser(subparsers, parent_parser):

    remote_subparsers = remote_parser.add_subparsers(
        dest="cmd",
-        help="Use dvc remote CMD --help for " "command-specific help.",
+        help="Use `dvc remote CMD --help` for " "command-specific help.",
    )

    fix_subparsers(remote_subparsers)
@@ -101,7 +127,9 @@ def add_parser(subparsers, parent_parser):
    remote_add_parser.add_argument("name", help="Name of the remote")
    remote_add_parser.add_argument(
        "url",
-        help="URL. See full list of supported urls at " "man.dvc.org/remote",
+        help="URL. See full list of supported urls at {}".format(
+            format_link("https://man.dvc.org/remote")
+        ),
    )
    remote_add_parser.add_argument(
        "-d",
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging
 import os
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,9 +1,6 @@
-from __future__ import unicode_literals
-
 import logging

 from dvc.command.data_sync import CmdDataBase
-from dvc.utils.compat import str


 logger = logging.getLogger(__name__)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import argparse
 import logging

@@ -16,7 +14,7 @@ class CmdUpdate(CmdBase):
        ret = 0
        for target in self.args.targets:
            try:
-                self.repo.update(target)
+                self.repo.update(target, self.args.rev)
            except DvcException:
                logger.exception("failed to update '{}'.".format(target))
                ret = 1
@@ -35,4 +33,7 @@ def add_parser(subparsers, parent_parser):
    update_parser.add_argument(
        "targets", nargs="+", help="DVC-files to update."
    )
+    update_parser.add_argument(
+        "--rev", nargs="?", help="Git revision (e.g. SHA, branch, tag)"
+    )
    update_parser.set_defaults(func=CmdUpdate)
@@ -1,11 +1,10 @@
-from __future__ import unicode_literals
-
 import argparse
 import itertools
 import logging
 import os
 import platform
 import uuid
+import pathlib

 try:
    import psutil
@@ -13,7 +12,6 @@ except ImportError:
    psutil = None

 from dvc.utils import is_binary, relpath
-from dvc.utils.compat import pathlib
 from dvc.command.base import CmdBaseNoRepo, append_doc_link
 from dvc.version import __version__
 from dvc.exceptions import DvcException, NotDvcRepoError
@@ -27,23 +25,13 @@ class CmdVersion(CmdBaseNoRepo):
    def run(self):
        from dvc.repo import Repo

-        dvc_version = __version__
-        python_version = platform.python_version()
-        platform_type = platform.platform()
-        binary = is_binary()
-        info = (
-            "DVC version: {dvc_version}\n"
-            "Python version: {python_version}\n"
-            "Platform: {platform_type}\n"
-            "Binary: {binary}\n"
-            "Package: {package}\n"
-        ).format(
-            dvc_version=dvc_version,
-            python_version=python_version,
-            platform_type=platform_type,
-            binary=binary,
-            package=PKG,
-        )
+        info = [
+            "DVC version: {}".format(__version__),
+            "Python version: {}".format(platform.python_version()),
+            "Platform: {}".format(platform.platform()),
+            "Binary: {}".format(is_binary()),
+            "Package: {}".format(PKG),
+        ]

        try:
            repo = Repo()
@@ -54,9 +42,14 @@ class CmdVersion(CmdBaseNoRepo):
            # later decides to enable shared cache mode with
            # `dvc config cache.shared group`.
            if os.path.exists(repo.cache.local.cache_dir):
-                info += "Cache: {cache}\n".format(
-                    cache=self.get_linktype_support_info(repo)
+                info.append(
+                    "Cache: {}".format(self.get_linktype_support_info(repo))
                )
+                if psutil:
+                    fs_type = self.get_fs_type(repo.cache.local.cache_dir)
+                    info.append(
+                        "Filesystem type (cache directory): {}".format(fs_type)
+                    )
            else:
                logger.warning(
                    "Unable to detect supported link types, as cache "
@@ -66,19 +59,14 @@ class CmdVersion(CmdBaseNoRepo):
                    "check.".format(relpath(repo.cache.local.cache_dir))
                )

-            if psutil:
-                info += (
-                    "Filesystem type (cache directory): {fs_cache}\n"
-                ).format(fs_cache=self.get_fs_type(repo.cache.local.cache_dir))
        except NotDvcRepoError:
            root_directory = os.getcwd()

        if psutil:
-            info += ("Filesystem type (workspace): {fs_root}").format(
-                fs_root=self.get_fs_type(os.path.abspath(root_directory))
-            )
+            fs_root = self.get_fs_type(os.path.abspath(root_directory))
+            info.append("Filesystem type (workspace): {}".format(fs_root))

-        logger.info(info)
+        logger.info("\n".join(info))
        return 0

    @staticmethod
@@ -98,9 +86,9 @@ class CmdVersion(CmdBaseNoRepo):
    @staticmethod
    def get_linktype_support_info(repo):
        links = {
-            "reflink": System.reflink,
-            "hardlink": System.hardlink,
-            "symlink": System.symlink,
+            "reflink": (System.reflink, None),
+            "hardlink": (System.hardlink, System.is_hardlink),
+            "symlink": (System.symlink, System.is_symlink),
        }

        fname = "." + str(uuid.uuid4())
@@ -110,18 +98,16 @@ class CmdVersion(CmdBaseNoRepo):

        cache = []

-        for name, link in links.items():
+        for name, (link, is_link) in links.items():
            try:
                link(src, dst)
+                status = "supported"
+                if is_link and not is_link(dst):
+                    status = "broken"
                os.unlink(dst)
-                supported = True
            except DvcException:
-                supported = False
-            cache.append(
-                "{name} - {supported}".format(
-                    name=name, supported=True if supported else False
-                )
-            )
+                status = "not supported"
+            cache.append("{name} - {status}".format(name=name, status=status))
        os.remove(src)

        return ", ".join(cache)
@@ -0,0 +1,42 @@
+"""Python version compatibility code"""
+
+# Backport os.fspath() from Python 3.6
+try:
+    from os import fspath  # noqa: F821
+
+    fspath_py35 = lambda s: s  # noqa: E731
+except ImportError:
+
+    def fspath(path):
+        """Return the path representation of a path-like object.
+
+        If str or bytes is passed in, it is returned unchanged. Otherwise the
+        os.PathLike interface is used to get the path representation. If the
+        path representation is not str or bytes, TypeError is raised. If the
+        provided path is not str, bytes, or os.PathLike, TypeError is raised.
+        """
+        if isinstance(path, (str, bytes)):
+            return path
+
+        # Work from the object's type to match method resolution of other magic
+        # methods.
+        path_type = type(path)
+        try:
+            path_repr = path_type.__fspath__(path)
+        except AttributeError:
+            if hasattr(path_type, "__fspath__"):
+                raise
+            else:
+                raise TypeError(
+                    "expected str, bytes or os.PathLike object, "
+                    "not " + path_type.__name__
+                )
+        if isinstance(path_repr, (str, bytes)):
+            return path_repr
+        else:
+            raise TypeError(
+                "expected {}.__fspath__() to return str or bytes, "
+                "not {}".format(path_type.__name__, type(path_repr).__name__)
+            )
+
+    fspath_py35 = fspath
@@ -1,47 +1,30 @@
 """DVC config objects."""
-from __future__ import unicode_literals
-
-import copy
-import errno
+from contextlib import contextmanager
 import logging
 import os
 import re
+from urllib.parse import urlparse

+from funcy import cached_property, re_find, walk_values, compact
 import configobj
-from voluptuous import Schema, Required, Optional, Invalid
-from voluptuous import All, Any, Lower, Range, Coerce, Match
+from voluptuous import Schema, Optional, Invalid, ALLOW_EXTRA
+from voluptuous import All, Any, Lower, Range, Coerce

-from dvc.exceptions import DvcException
-from dvc.exceptions import NotDvcRepoError
-from dvc.utils.compat import open, str
+from dvc.exceptions import DvcException, NotDvcRepoError
+from dvc.utils import relpath

 logger = logging.getLogger(__name__)


 class ConfigError(DvcException):
-    """DVC config exception.
+    """DVC config exception."""

-    Args:
-        msg (str): error message.
-        cause (Exception): optional exception that has caused this error.
-    """
-
-    def __init__(self, msg, cause=None):
-        super(ConfigError, self).__init__(
-            "config file error: {}".format(msg), cause=cause
-        )
+    def __init__(self, msg):
+        super().__init__("config file error: {}".format(msg))


 class NoRemoteError(ConfigError):
-    def __init__(self, command, cause=None):
-        msg = (
-            "no remote specified. Setup default remote with\n"
-            "    dvc config core.remote <name>\n"
-            "or use:\n"
-            "    dvc {} -r <name>\n".format(command)
-        )
-
-        super(NoRemoteError, self).__init__(msg, cause=cause)
+    pass


 def supported_cache_type(types):
@@ -65,13 +48,12 @@ def supported_cache_type(types):


 # Checks that value is either true or false and converts it to bool
-Bool = All(
+to_bool = Bool = All(
    Lower,
    Any("true", "false"),
    lambda v: v == "true",
    msg="expected true or false",
 )
-to_bool = Schema(Bool)


 def Choices(*choices):
@@ -84,8 +66,125 @@ def Choices(*choices):
    return Any(*choices, msg="expected one of {}".format(", ".join(choices)))


-class Config(object):  # pylint: disable=too-many-instance-attributes
-    """Class that manages configuration files for a dvc repo.
+def ByUrl(mapping):
+    schemas = walk_values(Schema, mapping)
+
+    def validate(data):
+        if "url" not in data:
+            raise Invalid("expected 'url'")
+
+        parsed = urlparse(data["url"])
+        # Windows absolute paths should really have scheme == "" (local)
+        if os.name == "nt" and len(parsed.scheme) == 1 and parsed.netloc == "":
+            return schemas[""](data)
+        if parsed.scheme not in schemas:
+            raise Invalid("Unsupported URL type {}://".format(parsed.scheme))
+
+        return schemas[parsed.scheme](data)
+
+    return validate
+
+
+class RelPath(str):
+    pass
+
+
+REMOTE_COMMON = {
+    "url": str,
+    "checksum_jobs": All(Coerce(int), Range(1)),
+    "no_traverse": Bool,
+    "verify": Bool,
+}
+LOCAL_COMMON = {
+    "type": supported_cache_type,
+    Optional("protected", default=False): Bool,
+    "shared": All(Lower, Choices("group")),
+    Optional("slow_link_warning", default=True): Bool,
+}
+SCHEMA = {
+    "core": {
+        "remote": Lower,
+        "checksum_jobs": All(Coerce(int), Range(1)),
+        Optional("interactive", default=False): Bool,
+        Optional("analytics", default=True): Bool,
+        Optional("hardlink_lock", default=False): Bool,
+    },
+    "cache": {
+        "local": str,
+        "s3": str,
+        "gs": str,
+        "hdfs": str,
+        "ssh": str,
+        "azure": str,
+        # This is for default local cache
+        "dir": str,
+        **LOCAL_COMMON,
+    },
+    "remote": {
+        str: ByUrl(
+            {
+                "": {**LOCAL_COMMON, **REMOTE_COMMON},
+                "s3": {
+                    "region": str,
+                    "profile": str,
+                    "credentialpath": str,
+                    "endpointurl": str,
+                    Optional("listobjects", default=False): Bool,
+                    Optional("use_ssl", default=True): Bool,
+                    "sse": str,
+                    "acl": str,
+                    "grant_read": str,
+                    "grant_read_acp": str,
+                    "grant_write_acp": str,
+                    "grant_full_control": str,
+                    **REMOTE_COMMON,
+                },
+                "gs": {
+                    "projectname": str,
+                    "credentialpath": str,
+                    **REMOTE_COMMON,
+                },
+                "ssh": {
+                    "type": supported_cache_type,
+                    "port": Coerce(int),
+                    "user": str,
+                    "password": str,
+                    "ask_password": Bool,
+                    "keyfile": str,
+                    "timeout": Coerce(int),
+                    "gss_auth": Bool,
+                    **REMOTE_COMMON,
+                },
+                "hdfs": {"user": str, **REMOTE_COMMON},
+                "azure": {"connection_string": str, **REMOTE_COMMON},
+                "oss": {
+                    "oss_key_id": str,
+                    "oss_key_secret": str,
+                    "oss_endpoint": str,
+                    **REMOTE_COMMON,
+                },
+                "gdrive": {
+                    "gdrive_client_id": str,
+                    "gdrive_client_secret": str,
+                    "gdrive_user_credentials_file": str,
+                    **REMOTE_COMMON,
+                },
+                "http": REMOTE_COMMON,
+                "https": REMOTE_COMMON,
+                "remote": {str: object},  # Any of the above options are valid
+            }
+        )
+    },
+    "state": {
+        "row_limit": All(Coerce(int), Range(1)),
+        "row_cleanup_quota": All(Coerce(int), Range(0, 100)),
+    },
+}
+COMPILED_SCHEMA = Schema(SCHEMA)
+
+
+class Config(dict):
+    """Class that manages configuration files for a DVC repo.

    Args:
        dvc_dir (str): optional path to `.dvc` directory, that is used to
@@ -102,164 +201,14 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
    APPNAME = "dvc"
    APPAUTHOR = "iterative"

-    # NOTE: used internally in RemoteLOCAL to know config
-    # location, that url should resolved relative to.
-    PRIVATE_CWD = "_cwd"
+    # In the order they shadow each other
+    LEVELS = ("system", "global", "repo", "local")

    CONFIG = "config"
    CONFIG_LOCAL = "config.local"

-    CREDENTIALPATH = "credentialpath"
-
-    LEVEL_LOCAL = 0
-    LEVEL_REPO = 1
-    LEVEL_GLOBAL = 2
-    LEVEL_SYSTEM = 3
-
-    SECTION_CORE = "core"
-    SECTION_CORE_LOGLEVEL = "loglevel"
-    SECTION_CORE_LOGLEVEL_SCHEMA = All(
-        Lower, Choices("info", "debug", "warning", "error")
-    )
-    SECTION_CORE_REMOTE = "remote"
-    SECTION_CORE_INTERACTIVE = "interactive"
-    SECTION_CORE_ANALYTICS = "analytics"
-    SECTION_CORE_CHECKSUM_JOBS = "checksum_jobs"
-    SECTION_CORE_HARDLINK_LOCK = "hardlink_lock"
-
-    SECTION_CACHE = "cache"
-    SECTION_CACHE_DIR = "dir"
-    SECTION_CACHE_TYPE = "type"
-    SECTION_CACHE_PROTECTED = "protected"
-    SECTION_CACHE_SHARED = "shared"
-    SECTION_CACHE_SHARED_SCHEMA = All(Lower, Choices("group"))
-    SECTION_CACHE_LOCAL = "local"
-    SECTION_CACHE_S3 = "s3"
-    SECTION_CACHE_GS = "gs"
-    SECTION_CACHE_SSH = "ssh"
-    SECTION_CACHE_HDFS = "hdfs"
-    SECTION_CACHE_AZURE = "azure"
-    SECTION_CACHE_SLOW_LINK_WARNING = "slow_link_warning"
-    SECTION_CACHE_SCHEMA = {
-        SECTION_CACHE_LOCAL: str,
-        SECTION_CACHE_S3: str,
-        SECTION_CACHE_GS: str,
-        SECTION_CACHE_HDFS: str,
-        SECTION_CACHE_SSH: str,
-        SECTION_CACHE_AZURE: str,
-        SECTION_CACHE_DIR: str,
-        SECTION_CACHE_TYPE: supported_cache_type,
-        Optional(SECTION_CACHE_PROTECTED, default=False): Bool,
-        SECTION_CACHE_SHARED: SECTION_CACHE_SHARED_SCHEMA,
-        PRIVATE_CWD: str,
-        Optional(SECTION_CACHE_SLOW_LINK_WARNING, default=True): Bool,
-    }
-
-    SECTION_CORE_SCHEMA = {
-        SECTION_CORE_LOGLEVEL: SECTION_CORE_LOGLEVEL_SCHEMA,
-        SECTION_CORE_REMOTE: Lower,
-        Optional(SECTION_CORE_INTERACTIVE, default=False): Bool,
-        Optional(SECTION_CORE_ANALYTICS, default=True): Bool,
-        SECTION_CORE_CHECKSUM_JOBS: All(Coerce(int), Range(1)),
-        Optional(SECTION_CORE_HARDLINK_LOCK, default=False): Bool,
-    }
-
-    # aws specific options
-    SECTION_AWS_CREDENTIALPATH = CREDENTIALPATH
-    SECTION_AWS_ENDPOINT_URL = "endpointurl"
-    SECTION_AWS_LIST_OBJECTS = "listobjects"
-    SECTION_AWS_REGION = "region"
-    SECTION_AWS_PROFILE = "profile"
-    SECTION_AWS_USE_SSL = "use_ssl"
-    SECTION_AWS_SSE = "sse"
-    SECTION_AWS_ACL = "acl"
-    SECTION_AWS_GRANT_READ = "grant_read"
-    SECTION_AWS_GRANT_READ_ACP = "grant_read_acp"
-    SECTION_AWS_GRANT_WRITE_ACP = "grant_write_acp"
-    SECTION_AWS_GRANT_FULL_CONTROL = "grant_full_control"
-
-    # gcp specific options
-    SECTION_GCP_CREDENTIALPATH = CREDENTIALPATH
-    SECTION_GCP_PROJECTNAME = "projectname"
-
-    # azure specific option
-    SECTION_AZURE_CONNECTION_STRING = "connection_string"
-
-    # Alibabacloud oss options
-    SECTION_OSS_ACCESS_KEY_ID = "oss_key_id"
-    SECTION_OSS_ACCESS_KEY_SECRET = "oss_key_secret"
-    SECTION_OSS_ENDPOINT = "oss_endpoint"
-
-    # GDrive options
-    SECTION_GDRIVE_CLIENT_ID = "gdrive_client_id"
-    SECTION_GDRIVE_CLIENT_SECRET = "gdrive_client_secret"
-    SECTION_GDRIVE_USER_CREDENTIALS_FILE = "gdrive_user_credentials_file"
-
-    SECTION_REMOTE_REGEX = r'^\s*remote\s*"(?P<name>.*)"\s*$'
-    SECTION_REMOTE_FMT = 'remote "{}"'
-    SECTION_REMOTE_URL = "url"
-    SECTION_REMOTE_USER = "user"
-    SECTION_REMOTE_PORT = "port"
-    SECTION_REMOTE_KEY_FILE = "keyfile"
-    SECTION_REMOTE_TIMEOUT = "timeout"
-    SECTION_REMOTE_PASSWORD = "password"
-    SECTION_REMOTE_ASK_PASSWORD = "ask_password"
-    SECTION_REMOTE_GSS_AUTH = "gss_auth"
-    SECTION_REMOTE_NO_TRAVERSE = "no_traverse"
-    SECTION_REMOTE_SCHEMA = {
-        Required(SECTION_REMOTE_URL): str,
-        SECTION_AWS_REGION: str,
-        SECTION_AWS_PROFILE: str,
-        SECTION_AWS_CREDENTIALPATH: str,
-        SECTION_AWS_ENDPOINT_URL: str,
-        Optional(SECTION_AWS_LIST_OBJECTS, default=False): Bool,
-        Optional(SECTION_AWS_USE_SSL, default=True): Bool,
-        SECTION_AWS_SSE: str,
-        SECTION_AWS_ACL: str,
-        SECTION_AWS_GRANT_READ: str,
-        SECTION_AWS_GRANT_READ_ACP: str,
-        SECTION_AWS_GRANT_WRITE_ACP: str,
-        SECTION_AWS_GRANT_FULL_CONTROL: str,
-        SECTION_GCP_PROJECTNAME: str,
-        SECTION_CACHE_TYPE: supported_cache_type,
-        Optional(SECTION_CACHE_PROTECTED, default=False): Bool,
-        SECTION_REMOTE_USER: str,
-        SECTION_REMOTE_PORT: Coerce(int),
-        SECTION_REMOTE_KEY_FILE: str,
-        SECTION_REMOTE_TIMEOUT: Coerce(int),
-        SECTION_REMOTE_PASSWORD: str,
-        SECTION_REMOTE_ASK_PASSWORD: Bool,
-        SECTION_REMOTE_GSS_AUTH: Bool,
-        SECTION_AZURE_CONNECTION_STRING: str,
-        SECTION_OSS_ACCESS_KEY_ID: str,
-        SECTION_OSS_ACCESS_KEY_SECRET: str,
-        SECTION_OSS_ENDPOINT: str,
-        SECTION_GDRIVE_CLIENT_ID: str,
-        SECTION_GDRIVE_CLIENT_SECRET: str,
-        SECTION_GDRIVE_USER_CREDENTIALS_FILE: str,
-        PRIVATE_CWD: str,
-        Optional(SECTION_REMOTE_NO_TRAVERSE, default=True): Bool,
-    }
-
-    SECTION_STATE = "state"
-    SECTION_STATE_ROW_LIMIT = "row_limit"
-    SECTION_STATE_ROW_CLEANUP_QUOTA = "row_cleanup_quota"
-    SECTION_STATE_SCHEMA = {
-        SECTION_STATE_ROW_LIMIT: All(Coerce(int), Range(1)),
-        SECTION_STATE_ROW_CLEANUP_QUOTA: All(Coerce(int), Range(0, 100)),
-    }
-
-    SCHEMA = {
-        Optional(SECTION_CORE, default={}): SECTION_CORE_SCHEMA,
-        Match(SECTION_REMOTE_REGEX): SECTION_REMOTE_SCHEMA,
-        Optional(SECTION_CACHE, default={}): SECTION_CACHE_SCHEMA,
-        Optional(SECTION_STATE, default={}): SECTION_STATE_SCHEMA,
-    }
-    COMPILED_SCHEMA = Schema(SCHEMA)
-
    def __init__(self, dvc_dir=None, validate=True):
        self.dvc_dir = dvc_dir
-        self.validate = validate

        if not dvc_dir:
            try:
@@ -271,33 +220,31 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
        else:
            self.dvc_dir = os.path.abspath(os.path.realpath(dvc_dir))

-        self.load()
+        self.load(validate=validate)

-    @staticmethod
-    def get_global_config_dir():
-        """Returns global config location. E.g. ~/.config/dvc/config.
+    @classmethod
+    def get_dir(cls, level):
+        from appdirs import user_config_dir, site_config_dir

-        Returns:
-            str: path to the global config directory.
-        """
-        from appdirs import user_config_dir
+        assert level in ("global", "system")

-        return user_config_dir(
-            appname=Config.APPNAME, appauthor=Config.APPAUTHOR
-        )
+        if level == "global":
+            return user_config_dir(cls.APPNAME, cls.APPAUTHOR)
+        if level == "system":
+            return site_config_dir(cls.APPNAME, cls.APPAUTHOR)

-    @staticmethod
-    def get_system_config_dir():
-        """Returns system config location. E.g. /etc/dvc.conf.
+    @cached_property
+    def files(self):
+        files = {
+            level: os.path.join(self.get_dir(level), self.CONFIG)
+            for level in ("system", "global")
+        }

-        Returns:
-            str: path to the system config directory.
-        """
-        from appdirs import site_config_dir
+        if self.dvc_dir is not None:
+            files["repo"] = os.path.join(self.dvc_dir, self.CONFIG)
+            files["local"] = os.path.join(self.dvc_dir, self.CONFIG_LOCAL)

-        return site_config_dir(
-            appname=Config.APPNAME, appauthor=Config.APPAUTHOR
-        )
+        return files

    @staticmethod
    def init(dvc_dir):
@@ -313,243 +260,137 @@ class Config(object):  # pylint: disable=too-many-instance-attributes
        open(config_file, "w+").close()
        return Config(dvc_dir)

-    def _resolve_cache_path(self, config):
-        cache = config.get(self.SECTION_CACHE)
-        if cache is None:
-            return
-
-        cache_dir = cache.get(self.SECTION_CACHE_DIR)
-        if cache_dir is None:
-            return
-
-        cache[self.PRIVATE_CWD] = os.path.dirname(config.filename)
-
-    def _resolve_paths(self, config):
-        if config.filename is None:
-            return config
-
-        ret = copy.deepcopy(config)
-        self._resolve_cache_path(ret)
-
-        for section in ret.values():
-            if self.SECTION_REMOTE_URL not in section.keys():
-                continue
-
-            section[self.PRIVATE_CWD] = os.path.dirname(ret.filename)
-
-        return ret
-
-    def _load_configs(self):
-        system_config_file = os.path.join(
-            self.get_system_config_dir(), self.CONFIG
-        )
-
-        global_config_file = os.path.join(
-            self.get_global_config_dir(), self.CONFIG
-        )
-
-        self._system_config = configobj.ConfigObj(system_config_file)
-        self._global_config = configobj.ConfigObj(global_config_file)
-        self._repo_config = configobj.ConfigObj()
-        self._local_config = configobj.ConfigObj()
-
-        if not self.dvc_dir:
-            return
-
-        config_file = os.path.join(self.dvc_dir, self.CONFIG)
-        config_local_file = os.path.join(self.dvc_dir, self.CONFIG_LOCAL)
-
-        self._repo_config = configobj.ConfigObj(config_file)
-        self._local_config = configobj.ConfigObj(config_local_file)
-
-    @property
-    def config_local_file(self):
-        return self._local_config.filename
-
-    @property
-    def config_file(self):
-        return self._repo_config.filename
-
-    def load(self):
+    def load(self, validate=True):
        """Loads config from all the config files.

        Raises:
            dvc.config.ConfigError: thrown if config has invalid format.
        """
-        self._load_configs()
+        conf = {}
+        for level in self.LEVELS:
+            if level in self.files:
+                _merge(conf, self.load_one(level))

-        self.config = configobj.ConfigObj()
-        for c in [
-            self._system_config,
-            self._global_config,
-            self._repo_config,
-            self._local_config,
-        ]:
-            c = self._resolve_paths(c)
-            c = self._lower(c)
-            self.config.merge(c)
+        if validate:
+            conf = self.validate(conf)

-        if not self.validate:
-            return
+        self.clear()
+        self.update(conf)

-        d = self.config.dict()
-        try:
-            d = self.COMPILED_SCHEMA(d)
-        except Invalid as exc:
-            raise ConfigError(str(exc), cause=exc)
-        self.config = configobj.ConfigObj(d, write_empty_values=True)
+        # Add resolved default cache.dir
+        if not self["cache"].get("dir") and self.dvc_dir:
+            self["cache"]["dir"] = os.path.join(self.dvc_dir, "cache")

-    def save(self, config=None):
-        """Saves config to config files.
+    def load_one(self, level):
+        conf = _load_config(self.files[level])
+        conf = self._load_paths(conf, self.files[level])

-        Raises:
-            dvc.config.ConfigError: thrown if failed to write config file.
-        """
-        if config is not None:
-            clist = [config]
-        else:
-            clist = [
-                self._system_config,
-                self._global_config,
-                self._repo_config,
-                self._local_config,
-            ]
+        # Autovivify sections
+        for key in COMPILED_SCHEMA.schema:
+            conf.setdefault(key, {})

-        for conf in clist:
-            self._save(conf)
+        return conf

+    @staticmethod
+    def _load_paths(conf, filename):
+        abs_conf_dir = os.path.abspath(os.path.dirname(filename))
+
+        def resolve(path):
+            if os.path.isabs(path) or re.match(r"\w+://", path):
+                return path
+            return RelPath(os.path.join(abs_conf_dir, path))
+
+        return Config._map_dirs(conf, resolve)
+
+    @staticmethod
+    def _save_paths(conf, filename):
+        conf_dir = os.path.dirname(filename)
+
+        def rel(path):
+            if re.match(r"\w+://", path):
+                return path
+
+            if isinstance(path, RelPath) or not os.path.isabs(path):
+                return relpath(path, conf_dir)
+            return path
+
+        return Config._map_dirs(conf, rel)
+
+    @staticmethod
+    def _map_dirs(conf, func):
+        dirs_schema = {"cache": {"dir": func}, "remote": {str: {"url": func}}}
+        return Schema(dirs_schema, extra=ALLOW_EXTRA)(conf)
+
+    @contextmanager
+    def edit(self, level="repo"):
+        if level in {"repo", "local"} and self.dvc_dir is None:
+            raise ConfigError("Not inside a dvc repo")
+
+        conf = self.load_one(level)
+        yield conf
+
+        conf = self._save_paths(conf, self.files[level])
+        _save_config(self.files[level], conf)
        self.load()

    @staticmethod
-    def _save(config):
-        if config.filename is None:
-            return
-
-        logger.debug("Writing '{}'.".format(config.filename))
-        dname = os.path.dirname(os.path.abspath(config.filename))
+    def validate(data):
        try:
-            os.makedirs(dname)
-        except OSError as exc:
-            if exc.errno != errno.EEXIST:
-                raise
-        config.write()
+            return COMPILED_SCHEMA(data)
+        except Invalid as exc:
+            raise ConfigError(str(exc)) from None

-    def unset(self, section, opt=None, level=None, force=False):
-        """Unsets specified option and/or section in the config.

-        Args:
-            section (str): section name.
-            opt (str): optional option name.
-            level (int): config level to use.
-            force (bool): don't error-out even if section doesn't exist. False
-                by default.
+def _load_config(filename):
+    conf_obj = configobj.ConfigObj(filename)
+    return _parse_remotes(_lower_keys(conf_obj.dict()))

-        Raises:
-            dvc.config.ConfigError: thrown if section doesn't exist and
-                `force != True`.
-        """
-        config = self.get_configobj(level)

-        if section not in config.keys():
-            if force:
-                return
-            raise ConfigError("section '{}' doesn't exist".format(section))
+def _save_config(filename, conf_dict):
+    logger.debug("Writing '{}'.".format(filename))
+    os.makedirs(os.path.dirname(filename), exist_ok=True)

-        if opt:
-            if opt not in config[section].keys():
-                if force:
-                    return
-                raise ConfigError(
-                    "option '{}.{}' doesn't exist".format(section, opt)
-                )
-            del config[section][opt]
+    config = configobj.ConfigObj(_pack_remotes(conf_dict))
+    config.filename = filename
+    config.write()

-            if not config[section]:
-                del config[section]
+
+def _parse_remotes(conf):
+    result = {"remote": {}}
+
+    for section, val in conf.items():
+        name = re_find(r'^\s*remote\s*"(.*)"\s*$', section)
+        if name:
+            result["remote"][name] = val
        else:
-            del config[section]
+            result[section] = val

-        self.save(config)
+    return result

-    def set(self, section, opt, value, level=None, force=True):
-        """Sets specified option in the config.

-        Args:
-            section (str): section name.
-            opt (str): option name.
-            value: value to set option to.
-            level (int): config level to use.
-            force (bool): set option even if section already exists. True by
-                default.
+def _pack_remotes(conf):
+    # Drop empty sections
+    result = compact(conf)

-        Raises:
-            dvc.config.ConfigError: thrown if section already exists and
-                `force != True`.
+    # Transform remote.name -> 'remote "name"'
+    for name, val in conf["remote"].items():
+        result['remote "{}"'.format(name)] = val
+    result.pop("remote", None)

-        """
-        config = self.get_configobj(level)
+    return result

-        if section not in config.keys():
-            config[section] = {}
-        elif not force:
-            raise ConfigError(
-                "Section '{}' already exists. Use `-f|--force` to overwrite "
-                "section with new value.".format(section)
-            )

-        config[section][opt] = value
-        self.save(config)
+def _merge(into, update):
+    """Merges second dict into first recursively"""
+    for key, val in update.items():
+        if isinstance(into.get(key), dict) and isinstance(val, dict):
+            _merge(into[key], val)
+        else:
+            into[key] = val

-    def get(self, section, opt=None, level=None):
-        """Return option value from the config.

-        Args:
-            section (str): section name.
-            opt (str): option name.
-            level (int): config level to use.
-
-        Returns:
-            value (str, int): option value.
-        """
-        config = self.get_configobj(level)
-
-        if section not in config.keys():
-            raise ConfigError("section '{}' doesn't exist".format(section))
-
-        if opt not in config[section].keys():
-            raise ConfigError(
-                "option '{}.{}' doesn't exist".format(section, opt)
-            )
-
-        return config[section][opt]
-
-    @staticmethod
-    def _lower(config):
-        new_config = configobj.ConfigObj()
-        for s_key, s_value in config.items():
-            new_s = {}
-            for key, value in s_value.items():
-                new_s[key.lower()] = str(value)
-            new_config[s_key.lower()] = new_s
-        return new_config
-
-    def get_configobj(self, level):
-        configs = {
-            self.LEVEL_LOCAL: self._local_config,
-            self.LEVEL_REPO: self._repo_config,
-            self.LEVEL_GLOBAL: self._global_config,
-            self.LEVEL_SYSTEM: self._system_config,
-        }
-
-        return configs.get(level, self._repo_config)
-
-    def list_options(self, section_regex, option, level=None):
-        ret = {}
-        config = self.get_configobj(level)
-        for section in config.keys():
-            r = re.match(section_regex, section)
-            if r:
-                name = r.group("name")
-                value = config[section].get(option, "")
-                ret[name] = value
-        return ret
+def _lower_keys(data):
+    return {
+        k.lower(): _lower_keys(v) if isinstance(v, dict) else v
+        for k, v in data.items()
+    }
@@ -1,5 +1,4 @@
 """Launch `dvc daemon` command in a separate detached process."""
-from __future__ import unicode_literals

 import inspect
 import logging
@@ -10,7 +9,6 @@ from subprocess import Popen
 from dvc.env import DVC_DAEMON
 from dvc.utils import fix_env
 from dvc.utils import is_binary
-from dvc.utils.compat import cast_bytes_py2


 logger = logging.getLogger(__name__)
@@ -99,9 +97,7 @@ def daemon(args):

    env = fix_env()
    file_path = os.path.abspath(inspect.stack()[0][1])
-    env[cast_bytes_py2("PYTHONPATH")] = cast_bytes_py2(
-        os.path.dirname(os.path.dirname(file_path))
-    )
-    env[cast_bytes_py2(DVC_DAEMON)] = cast_bytes_py2("1")
+    env["PYTHONPATH"] = os.path.dirname(os.path.dirname(file_path))
+    env[DVC_DAEMON] = "1"

    _spawn(cmd, env)
@@ -1,6 +1,4 @@
 """Draws DAG in ASCII."""
-from __future__ import print_function
-from __future__ import unicode_literals

 import logging
 import math
@@ -16,7 +14,7 @@ from grandalf.routing import EdgeViewer
 from grandalf.routing import route_with_lines

 from dvc.env import DVC_PAGER
-
+from dvc.utils import format_link

 logger = logging.getLogger(__name__)

@@ -47,7 +45,9 @@ def find_pager():

    logger.warning(
        "Unable to find `less` in the PATH. Check out "
-        "man.dvc.org/doc/command-reference/pipeline/show for more info."
+        "{} for more info.".format(
+            format_link("https://man.dvc.org/pipeline/show")
+        )
    )
    return pydoc.plainpager

@@ -1,9 +1,7 @@
 """Manages dvc remotes that user can use with push/pull/status commands."""
-from __future__ import unicode_literals

 import logging

-from dvc.config import Config
 from dvc.config import NoRemoteError
 from dvc.remote import Remote

@@ -25,22 +23,27 @@ class DataCloud(object):
    def __init__(self, repo):
        self.repo = repo

-    @property
-    def _config(self):
-        return self.repo.config.config
-
-    @property
-    def _core(self):
-        return self._config.get(Config.SECTION_CORE, {})
-
    def get_remote(self, remote=None, command="<command>"):
        if not remote:
-            remote = self._core.get(Config.SECTION_CORE_REMOTE)
+            remote = self.repo.config["core"].get("remote")

        if remote:
            return self._init_remote(remote)

-        raise NoRemoteError(command)
+        if bool(self.repo.config["remote"]):
+            error_msg = (
+                "no remote specified. Setup default remote with\n"
+                "    dvc remote default <remote name>\n"
+                "or use:\n"
+                "    dvc {} -r <remote name>".format(command)
+            )
+        else:
+            error_msg = (
+                "no remote specified. Create a default remote with\n"
+                "    dvc remote add -d <remote name> <remote url>"
+            )
+
+        raise NoRemoteError(error_msg)

    def _init_remote(self, remote):
        return Remote(self.repo, name=remote)
@@ -74,13 +77,25 @@ class DataCloud(object):
            show_checksums (bool): show checksums instead of file names in
                information messages.
        """
-        return self.repo.cache.local.pull(
-            cache,
-            jobs=jobs,
-            remote=self.get_remote(remote, "pull"),
-            show_checksums=show_checksums,
+        remote = self.get_remote(remote, "pull")
+        downloaded_items_num = self.repo.cache.local.pull(
+            cache, jobs=jobs, remote=remote, show_checksums=show_checksums
        )

+        if not remote.verify:
+            self._save_pulled_checksums(cache)
+
+        return downloaded_items_num
+
+    def _save_pulled_checksums(self, cache):
+        for checksum in cache["local"].keys():
+            cache_file = self.repo.cache.local.checksum_to_path_info(checksum)
+            if self.repo.cache.local.exists(cache_file):
+                # We can safely save here, as existing corrupted files will be
+                # removed upon status, while files corrupted during download
+                # will not be moved from tmp_file (see `RemoteBASE.download()`)
+                self.repo.state.save(cache_file, checksum)
+
    def status(self, cache, jobs=None, remote=None, show_checksums=False):
        """Check status of data items in a cloud-agnostic way.

@@ -1,4 +1,4 @@
-from __future__ import unicode_literals
+from urllib.parse import urlparse

 import dvc.output as output
 from dvc.dependency.gs import DependencyGS
@@ -46,8 +46,6 @@ SCHEMA[DependencyREPO.PARAM_REPO] = DependencyREPO.REPO_SCHEMA


 def _get(stage, p, info):
-    from dvc.utils.compat import urlparse
-
    parsed = urlparse(p)

    if parsed.scheme == "remote":
@@ -1,23 +1,21 @@
-from __future__ import unicode_literals
-
 from dvc.exceptions import DvcException


 class DependencyDoesNotExistError(DvcException):
    def __init__(self, path):
        msg = "dependency '{}' does not exist".format(path)
-        super(DependencyDoesNotExistError, self).__init__(msg)
+        super().__init__(msg)


 class DependencyIsNotFileOrDirError(DvcException):
    def __init__(self, path):
        msg = "dependency '{}' is not a file or directory".format(path)
-        super(DependencyIsNotFileOrDirError, self).__init__(msg)
+        super().__init__(msg)


 class DependencyIsStageFileError(DvcException):
    def __init__(self, path):
-        super(DependencyIsStageFileError, self).__init__(
+        super().__init__(
            "Stage file '{}' cannot be a dependency.".format(path)
        )

@@ -29,5 +27,5 @@ class DependencyBase(object):
    IsNotFileOrDirError = DependencyIsNotFileOrDirError
    IsStageFileError = DependencyIsStageFileError

-    def update(self):
+    def update(self, rev=None):
        pass
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.gs import OutputGS

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.hdfs import OutputHDFS

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.base import OutputBase
 from dvc.remote.http import RemoteHTTP
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from .http import DependencyHTTP
 from dvc.remote.https import RemoteHTTPS

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.local import OutputLOCAL

@@ -1,18 +1,10 @@
-from __future__ import unicode_literals
-
-import copy
 import os
-from contextlib import contextmanager
-from dvc.utils.compat import FileNotFoundError

-from funcy import merge
+from voluptuous import Required

 from .local import DependencyLOCAL
-from dvc.external_repo import external_repo
-from dvc.utils.compat import str
 from dvc.exceptions import OutputNotFoundError
-from dvc.exceptions import PathMissingError
-from dvc.utils.fs import fs_copy
+from dvc.path_info import PathInfo


 class DependencyREPO(DependencyLOCAL):
@@ -21,11 +13,15 @@ class DependencyREPO(DependencyLOCAL):
    PARAM_REV = "rev"
    PARAM_REV_LOCK = "rev_lock"

-    REPO_SCHEMA = {PARAM_URL: str, PARAM_REV: str, PARAM_REV_LOCK: str}
+    REPO_SCHEMA = {
+        Required(PARAM_URL): str,
+        PARAM_REV: str,
+        PARAM_REV_LOCK: str,
+    }

    def __init__(self, def_repo, stage, *args, **kwargs):
        self.def_repo = def_repo
-        super(DependencyREPO, self).__init__(stage, *args, **kwargs)
+        super().__init__(stage, *args, **kwargs)

    def _parse_path(self, remote, path):
        return None
@@ -37,24 +33,33 @@ class DependencyREPO(DependencyLOCAL):
    @property
    def repo_pair(self):
        d = self.def_repo
-        return d[self.PARAM_URL], d[self.PARAM_REV_LOCK] or d[self.PARAM_REV]
+        rev = d.get(self.PARAM_REV_LOCK) or d.get(self.PARAM_REV)
+        return d[self.PARAM_URL], rev

    def __str__(self):
        return "{} ({})".format(self.def_path, self.def_repo[self.PARAM_URL])

-    @contextmanager
-    def _make_repo(self, **overrides):
-        with external_repo(**merge(self.def_repo, overrides)) as repo:
-            yield repo
+    def _make_repo(self, *, locked=True):
+        from dvc.external_repo import external_repo
+
+        d = self.def_repo
+        rev = (d.get("rev_lock") if locked else None) or d.get("rev")
+        return external_repo(d["url"], rev=rev)
+
+    def _get_checksum(self, locked=True):
+        with self._make_repo(locked=locked) as repo:
+            try:
+                return repo.find_out_by_relpath(self.def_path).info["md5"]
+            except OutputNotFoundError:
+                path = PathInfo(os.path.join(repo.root_dir, self.def_path))
+                # We are polluting our repo cache with some dir listing here
+                return self.repo.cache.local.get_checksum(path)

    def status(self):
-        with self._make_repo() as repo:
-            current = repo.find_out_by_relpath(self.def_path).info
+        current_checksum = self._get_checksum(locked=True)
+        updated_checksum = self._get_checksum(locked=False)

-        with self._make_repo(rev_lock=None) as repo:
-            updated = repo.find_out_by_relpath(self.def_path).info
-
-        if current != updated:
+        if current_checksum != updated_checksum:
            return {str(self): "update available"}

        return {}
@@ -65,55 +70,19 @@ class DependencyREPO(DependencyLOCAL):
    def dumpd(self):
        return {self.PARAM_PATH: self.def_path, self.PARAM_REPO: self.def_repo}

-    def fetch(self):
-        with self._make_repo(
-            cache_dir=self.repo.cache.local.cache_dir
-        ) as repo:
-            self.def_repo[self.PARAM_REV_LOCK] = repo.scm.get_rev()
-
-            out = repo.find_out_by_relpath(self.def_path)
-            with repo.state:
-                repo.cloud.pull(out.get_used_cache())
-
-        return out
-
-    @staticmethod
-    def _is_git_file(repo, path):
-        if not os.path.isabs(path):
-            try:
-                output = repo.find_out_by_relpath(path)
-                if not output.use_cache:
-                    return True
-            except OutputNotFoundError:
-                return True
-        return False
-
-    def _copy_if_git_file(self, to_path):
-        src_path = self.def_path
-        with self._make_repo(
-            cache_dir=self.repo.cache.local.cache_dir
-        ) as repo:
-            if not self._is_git_file(repo, src_path):
-                return False
-
-            src_full_path = os.path.join(repo.root_dir, src_path)
-            dst_full_path = os.path.abspath(to_path)
-            fs_copy(src_full_path, dst_full_path)
-        return True
-
    def download(self, to):
-        try:
-            if self._copy_if_git_file(to.fspath):
-                return
+        with self._make_repo() as repo:
+            if self.def_repo.get(self.PARAM_REV_LOCK) is None:
+                self.def_repo[self.PARAM_REV_LOCK] = repo.scm.get_rev()

-            out = self.fetch()
-            to.info = copy.copy(out.info)
-            to.checkout()
-        except (FileNotFoundError):
-            raise PathMissingError(
-                self.def_path, self.def_repo[self.PARAM_URL]
-            )
+            if hasattr(repo, "cache"):
+                repo.cache.local.cache_dir = self.repo.cache.local.cache_dir

-    def update(self):
-        with self._make_repo(rev_lock=None) as repo:
+            repo.pull_to(self.def_path, to.path_info)
+
+    def update(self, rev=None):
+        if rev:
+            self.def_repo[self.PARAM_REV] = rev
+
+        with self._make_repo(locked=False) as repo:
            self.def_repo[self.PARAM_REV_LOCK] = repo.scm.get_rev()
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.s3 import OutputS3

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.dependency.base import DependencyBase
 from dvc.output.ssh import OutputSSH

@@ -1,32 +1,10 @@
 """Exceptions raised by the dvc."""
-from __future__ import unicode_literals

-import traceback
-
-from dvc.utils import relpath
-from dvc.utils.compat import builtin_str
-from dvc.utils.compat import str
+from dvc.utils import relpath, format_link


 class DvcException(Exception):
-    """Base class for all dvc exceptions.
-
-    Args:
-        msg (unicode): message for this exception.
-        cause (Exception): optional cause exception.
-    """
-
-    def __init__(self, msg, cause=None):
-        # NOTE: unlike python 3, python 2 doesn't have built-in support
-        # for chained exceptions, so we are using our own implementation.
-        self.cause = cause
-        self.cause_tb = None
-        if cause:
-            try:
-                self.cause_tb = traceback.format_exc()
-            except AttributeError:  # pragma: no cover
-                pass
-        super(DvcException, self).__init__(msg)
+    """Base class for all dvc exceptions."""


 class OutputDuplicationError(DvcException):
@@ -39,18 +17,14 @@ class OutputDuplicationError(DvcException):
    """

    def __init__(self, output, stages):
-        assert isinstance(output, str) or isinstance(output, builtin_str)
-        assert isinstance(stages, list)
-        assert all(
-            isinstance(stage, str) or isinstance(stage, builtin_str)
-            for stage in stages
-        )
+        assert isinstance(output, str)
+        assert all(hasattr(stage, "relpath") for stage in stages)
        msg = (
            "file/directory '{}' is specified as an output in more than one "
            "stage: {}\n"
            "This is not allowed. Consider using a different output name."
-        ).format(output, "\n    ".join(stages))
-        super(OutputDuplicationError, self).__init__(msg)
+        ).format(output, "\n    ".join(s.relpath for s in stages))
+        super().__init__(msg)


 class OutputNotFoundError(DvcException):
@@ -63,8 +37,8 @@ class OutputNotFoundError(DvcException):
    def __init__(self, output, repo=None):
        self.output = output
        self.repo = repo
-        super(OutputNotFoundError, self).__init__(
-            "unable to find DVC-file with output '{path}'".format(
+        super().__init__(
+            "Unable to find DVC-file with output '{path}'".format(
                path=relpath(self.output)
            )
        )
@@ -75,21 +49,17 @@ class StagePathAsOutputError(DvcException):
    an output of another stage.

    Args:
-        cwd (str): path to the directory.
-        fname (str): path to the DVC-file that has cwd specified as an
-            output.
+        stage (Stage): a stage that is in some other stages output
+        output (str): an output covering the stage above
    """

-    def __init__(self, wdir, fname):
-        assert isinstance(wdir, str) or isinstance(wdir, builtin_str)
-        assert isinstance(fname, str) or isinstance(fname, builtin_str)
-        msg = (
-            "current working directory '{cwd}' is specified as an output in "
-            "'{fname}'. Use another CWD to prevent any data removal.".format(
-                cwd=wdir, fname=fname
+    def __init__(self, stage, output):
+        assert isinstance(output, str)
+        super().__init__(
+            "'{stage}' is within an output '{output}' of another stage".format(
+                stage=stage.relpath, output=output
            )
        )
-        super(StagePathAsOutputError, self).__init__(msg)


 class CircularDependencyError(DvcException):
@@ -101,13 +71,13 @@ class CircularDependencyError(DvcException):
    """

    def __init__(self, dependency):
-        assert isinstance(dependency, (str, builtin_str))
+        assert isinstance(dependency, str)

        msg = (
            "file/directory '{}' is specified as an output and as a "
            "dependency."
        )
-        super(CircularDependencyError, self).__init__(msg.format(dependency))
+        super().__init__(msg.format(dependency))


 class ArgumentDuplicationError(DvcException):
@@ -119,9 +89,8 @@ class ArgumentDuplicationError(DvcException):
    """

    def __init__(self, path):
-        assert isinstance(path, (str, builtin_str))
-        msg = "file '{}' is specified more than once."
-        super(ArgumentDuplicationError, self).__init__(msg.format(path))
+        assert isinstance(path, str)
+        super().__init__("file '{}' is specified more than once.".format(path))


 class MoveNotDataSourceError(DvcException):
@@ -139,68 +108,55 @@ class MoveNotDataSourceError(DvcException):
            "it by hand, or remove '{path}' and create a new one at the "
            "desired location."
        )
-        super(MoveNotDataSourceError, self).__init__(msg.format(path=path))
+        super().__init__(msg.format(path=path))


 class NotDvcRepoError(DvcException):
-    """Thrown if a directory is not a dvc repo.
-
-    Args:
-        root (str): path to the directory.
-    """
-
-    def __init__(self, root):
-        msg = (
-            "you are not inside of a dvc repository "
-            "(checked up to mount point '{}')"
-        )
-        super(NotDvcRepoError, self).__init__(msg.format(root))
+    """Thrown if a directory is not a DVC repo"""


 class DvcParserError(DvcException):
    """Base class for CLI parser errors."""

    def __init__(self):
-        super(DvcParserError, self).__init__("parser error")
+        super().__init__("parser error")


 class CyclicGraphError(DvcException):
    def __init__(self, stages):
        assert isinstance(stages, list)
-        stages = "\n".join("\t- {}".format(stage) for stage in stages)
+        stages = "\n".join("\t- {}".format(stage.relpath) for stage in stages)
        msg = (
            "you've introduced a cycle in your pipeline that involves "
            "the following stages:"
            "\n"
            "{stages}".format(stages=stages)
        )
-        super(CyclicGraphError, self).__init__(msg)
+        super().__init__(msg)


 class ConfirmRemoveError(DvcException):
    def __init__(self, path):
-        super(ConfirmRemoveError, self).__init__(
+        super().__init__(
            "unable to remove '{}' without a confirmation from the user. Use "
            "`-f` to force.".format(path)
        )


 class InitError(DvcException):
-    def __init__(self, msg):
-        super(InitError, self).__init__(msg)
+    pass


 class ReproductionError(DvcException):
-    def __init__(self, dvc_file_name, ex):
+    def __init__(self, dvc_file_name):
        self.path = dvc_file_name
-        msg = "failed to reproduce '{}'".format(dvc_file_name)
-        super(ReproductionError, self).__init__(msg, cause=ex)
+        super().__init__("failed to reproduce '{}'".format(dvc_file_name))


 class BadMetricError(DvcException):
    def __init__(self, paths):
-        super(BadMetricError, self).__init__(
-            "the following metrics do not exists, "
+        super().__init__(
+            "the following metrics do not exist, "
            "are not metric files or are malformed: {paths}".format(
                paths=", ".join("'{}'".format(path) for path in paths)
            )
@@ -209,87 +165,71 @@ class BadMetricError(DvcException):

 class NoMetricsError(DvcException):
    def __init__(self):
-        super(NoMetricsError, self).__init__(
+        super().__init__(
            "no metric files in this repository. "
            "Use `dvc metrics add` to add a metric file to track."
        )


 class StageFileCorruptedError(DvcException):
-    def __init__(self, path, cause=None):
+    def __init__(self, path):
        path = relpath(path)
-        super(StageFileCorruptedError, self).__init__(
+        super().__init__(
            "unable to read DVC-file: {} "
-            "YAML file structure is corrupted".format(path),
-            cause=cause,
+            "YAML file structure is corrupted".format(path)
        )


 class RecursiveAddingWhileUsingFilename(DvcException):
    def __init__(self):
-        super(RecursiveAddingWhileUsingFilename, self).__init__(
+        super().__init__(
            "cannot use `fname` with multiple targets or `-R|--recursive`"
        )


 class OverlappingOutputPathsError(DvcException):
-    def __init__(self, out_1, out_2):
-        super(OverlappingOutputPathsError, self).__init__(
-            "Paths for outs:\n'{}'('{}')\n'{}'('{}')\noverlap. To avoid "
-            "unpredictable behaviour, rerun command with non overlapping outs "
-            "paths.".format(
-                str(out_1),
-                out_1.stage.relpath,
-                str(out_2),
-                out_2.stage.relpath,
-            )
-        )
+    def __init__(self, parent, overlapping_out, message):
+        self.parent = parent
+        self.overlapping_out = overlapping_out
+        super().__init__(message)


 class CheckoutErrorSuggestGit(DvcException):
-    def __init__(self, target, cause):
-        super(CheckoutErrorSuggestGit, self).__init__(
-            "Did you mean `git checkout {}`?".format(target), cause=cause
-        )
+    def __init__(self, target):
+        super().__init__("Did you mean `git checkout {}`?".format(target))


 class ETagMismatchError(DvcException):
    def __init__(self, etag, cached_etag):
-        super(ETagMismatchError, self).__init__(
+        super().__init__(
            "ETag mismatch detected when copying file to cache! "
            "(expected: '{}', actual: '{}')".format(etag, cached_etag)
        )


 class FileMissingError(DvcException):
-    def __init__(self, path, cause=None):
-        super(FileMissingError, self).__init__(
-            "Can't find '{}' neither locally nor on remote".format(path),
-            cause=cause,
+    def __init__(self, path):
+        self.path = path
+        super().__init__(
+            "Can't find '{}' neither locally nor on remote".format(path)
        )


 class DvcIgnoreInCollectedDirError(DvcException):
    def __init__(self, ignore_dirname):
-        super(DvcIgnoreInCollectedDirError, self).__init__(
+        super().__init__(
            ".dvcignore file should not be in collected dir path: "
            "'{}'".format(ignore_dirname)
        )


-class UrlNotDvcRepoError(DvcException):
-    def __init__(self, url):
-        super(UrlNotDvcRepoError, self).__init__(
-            "URL '{}' is not a dvc repository.".format(url)
-        )
-
-
 class GitHookAlreadyExistsError(DvcException):
    def __init__(self, hook_name):
-        super(GitHookAlreadyExistsError, self).__init__(
-            "Hook '{}' already exists. Please refer to "
-            "https://man.dvc.org/install "
-            "for more info.".format(hook_name)
+        super().__init__(
+            "Hook '{}' already exists. Please refer to {} for more "
+            "info.".format(
+                hook_name, format_link("https://man.dvc.org/install")
+            )
        )


@@ -297,7 +237,7 @@ class DownloadError(DvcException):
    def __init__(self, amount):
        self.amount = amount

-        super(DownloadError, self).__init__(
+        super().__init__(
            "{amount} files failed to download".format(amount=amount)
        )

@@ -306,7 +246,7 @@ class UploadError(DvcException):
    def __init__(self, amount):
        self.amount = amount

-        super(UploadError, self).__init__(
+        super().__init__(
            "{amount} files failed to upload".format(amount=amount)
        )

@@ -318,7 +258,7 @@ class CheckoutError(DvcException):
            "Checkout failed for following targets:\n {}\nDid you "
            "forget to fetch?".format("\n".join(targets))
        )
-        super(CheckoutError, self).__init__(m)
+        super().__init__(m)


 class CollectCacheError(DvcException):
@@ -327,14 +267,14 @@ class CollectCacheError(DvcException):

 class NoRemoteInExternalRepoError(DvcException):
    def __init__(self, url):
-        super(NoRemoteInExternalRepoError, self).__init__(
+        super().__init__(
            "No DVC remote is specified in target repository '{}'.".format(url)
        )


 class NoOutputInExternalRepoError(DvcException):
    def __init__(self, path, external_repo_path, external_repo_url):
-        super(NoOutputInExternalRepoError, self).__init__(
+        super().__init__(
            "Output '{}' not found in target repository '{}'".format(
                relpath(path, external_repo_path), external_repo_url
            )
@@ -343,13 +283,39 @@ class NoOutputInExternalRepoError(DvcException):

 class HTTPError(DvcException):
    def __init__(self, code, reason):
-        super(HTTPError, self).__init__("'{} {}'".format(code, reason))
+        super().__init__("'{} {}'".format(code, reason))


 class PathMissingError(DvcException):
-    def __init__(self, path, repo):
+    default_msg = (
+        "The path '{}' does not exist in the target repository '{}'"
+        " neither as an output nor a git-handled file."
+    )
+    default_msg_output_only = (
+        "The path '{}' does not exist in the target repository '{}'"
+        " as an output."
+    )
+
+    def __init__(self, path, repo, output_only=False):
        msg = (
-            "The path '{}' does not exist in the target repository '{}'"
-            " neighther as an output nor a git-handled file."
+            self.default_msg
+            if not output_only
+            else self.default_msg_output_only
+        )
+        super().__init__(msg.format(path, repo))
+        self.output_only = output_only
+
+
+class RemoteCacheRequiredError(DvcException):
+    def __init__(self, path_info):
+        super().__init__(
+            (
+                "Current operation was unsuccessful because '{}' requires "
+                "existing cache on '{}' remote. See {} for information on how "
+                "to set up remote cache."
+            ).format(
+                path_info,
+                path_info.scheme,
+                format_link("https://man.dvc.org/config#cache"),
+            )
        )
-        super(PathMissingError, self).__init__(msg.format(path, repo))
@@ -1,29 +1,36 @@
-from __future__ import unicode_literals
-
+import logging
 import os
 import tempfile
 from contextlib import contextmanager
 from distutils.dir_util import copy_tree
+import threading

-from funcy import retry
+from funcy import retry, suppress, wrap_with, cached_property

-from dvc.config import NoRemoteError, ConfigError
+from dvc.path_info import PathInfo
+from dvc.compat import fspath
+from dvc.repo import Repo
+from dvc.config import NoRemoteError, NotDvcRepoError
 from dvc.exceptions import NoRemoteInExternalRepoError
-from dvc.remote import RemoteConfig
-from dvc.exceptions import NoOutputInExternalRepoError
-from dvc.exceptions import OutputNotFoundError
-from dvc.utils.fs import remove
+from dvc.exceptions import OutputNotFoundError, NoOutputInExternalRepoError
+from dvc.exceptions import FileMissingError, PathMissingError
+from dvc.utils.fs import remove, fs_copy, move
+from dvc.utils import tmp_fname
+from dvc.scm.git import Git


-REPO_CACHE = {}
+logger = logging.getLogger(__name__)


@contextmanager
-def external_repo(url=None, rev=None, rev_lock=None, cache_dir=None):
-    from dvc.repo import Repo
+def external_repo(url, rev=None, for_write=False):
+    logger.debug("Creating external repo {}@{}", url, rev)
+    path = _cached_clone(url, rev, for_write=for_write)
+    try:
+        repo = ExternalRepo(path, url)
+    except NotDvcRepoError:
+        repo = ExternalGitRepo(path, url)

-    path = _external_repo(url=url, rev=rev_lock or rev, cache_dir=cache_dir)
-    repo = Repo(path)
    try:
        yield repo
    except NoRemoteError:
@@ -32,90 +39,206 @@ def external_repo(url=None, rev=None, rev_lock=None, cache_dir=None):
        if exc.repo is repo:
            raise NoOutputInExternalRepoError(exc.output, repo.root_dir, url)
        raise
-    repo.close()
-
-
-def _external_repo(url=None, rev=None, cache_dir=None):
-    from dvc.config import Config
-    from dvc.cache import CacheConfig
-    from dvc.repo import Repo
-
-    key = (url, rev, cache_dir)
-    if key in REPO_CACHE:
-        return REPO_CACHE[key]
-
-    new_path = tempfile.mkdtemp("dvc-erepo")
-
-    # Copy and adjust existing clone
-    if (url, None, None) in REPO_CACHE:
-        old_path = REPO_CACHE[url, None, None]
-
-        # This one unlike shutil.copytree() works with an existing dir
-        copy_tree(old_path, new_path)
-    else:
-        # Create a new clone
-        _clone_repo(url, new_path)
-
-        # Save clean clone dir so that we will have access to a default branch
-        clean_clone_path = tempfile.mkdtemp("dvc-erepo")
-        copy_tree(new_path, clean_clone_path)
-        REPO_CACHE[url, None, None] = clean_clone_path
-
-    # Adjust new clone/copy to fit rev and cache_dir
-
-    # Checkout needs to be done first because current branch might not be
-    # DVC repository
-    if rev is not None:
-        _git_checkout(new_path, rev)
-
-    repo = Repo(new_path)
-    try:
-        # check if the URL is local and no default remote is present
-        # add default remote pointing to the original repo's cache location
-        if os.path.isdir(url):
-            rconfig = RemoteConfig(repo.config)
-            if not _default_remote_set(rconfig):
-                original_repo = Repo(url)
-                try:
-                    rconfig.add(
-                        "auto-generated-upstream",
-                        original_repo.cache.local.cache_dir,
-                        default=True,
-                        level=Config.LEVEL_LOCAL,
-                    )
-                finally:
-                    original_repo.close()
-
-        if cache_dir is not None:
-            cache_config = CacheConfig(repo.config)
-            cache_config.set_dir(cache_dir, level=Config.LEVEL_LOCAL)
+    except FileMissingError as exc:
+        raise PathMissingError(exc.path, url)
    finally:
-        # Need to close/reopen repo to force config reread
        repo.close()
-
-    REPO_CACHE[key] = new_path
-    return new_path
+        if for_write:
+            _remove(path)


-def _git_checkout(repo_path, revision):
-    from dvc.scm import Git
-
-    git = Git(repo_path)
-    try:
-        git.checkout(revision)
-    finally:
-        git.close()
+CLONES = {}
+CACHE_DIRS = {}


 def clean_repos():
    # Outside code should not see cache while we are removing
-    repo_paths = list(REPO_CACHE.values())
-    REPO_CACHE.clear()
+    paths = list(CLONES.values()) + list(CACHE_DIRS.values())
+    CLONES.clear()
+    CACHE_DIRS.clear()

-    for path in repo_paths:
+    for path in paths:
        _remove(path)


+class ExternalRepo(Repo):
+    def __init__(self, root_dir, url):
+        super().__init__(root_dir)
+        self.url = url
+        self._set_cache_dir()
+        self._set_upstream()
+
+    def pull_to(self, path, to_info):
+        """
+        Pull the corresponding file or directory specified by `path` and
+        checkout it into `to_info`.
+
+        It works with files tracked by Git and DVC, and also local files
+        outside the repository.
+        """
+        out = None
+        path_info = PathInfo(self.root_dir) / path
+
+        with suppress(OutputNotFoundError):
+            (out,) = self.find_outs_by_path(fspath(path_info), strict=False)
+
+        try:
+            if out and out.use_cache:
+                self._pull_cached(out, path_info, to_info)
+                return
+
+            # Check if it is handled by Git (it can't have an absolute path)
+            if os.path.isabs(path):
+                raise FileNotFoundError
+
+            fs_copy(fspath(path_info), fspath(to_info))
+        except FileNotFoundError:
+            raise PathMissingError(path, self.url)
+
+    def _pull_cached(self, out, path_info, dest):
+        with self.state:
+            tmp = PathInfo(tmp_fname(dest))
+            src = tmp / path_info.relative_to(out.path_info)
+
+            out.path_info = tmp
+
+            # Only pull unless all needed cache is present
+            if out.changed_cache(filter_info=src):
+                self.cloud.pull(out.get_used_cache(filter_info=src))
+
+            failed = out.checkout(filter_info=src)
+
+            move(src, dest)
+            remove(tmp)
+
+            if failed:
+                raise FileNotFoundError
+
+    @wrap_with(threading.Lock())
+    def _set_cache_dir(self):
+        try:
+            cache_dir = CACHE_DIRS[self.url]
+        except KeyError:
+            cache_dir = CACHE_DIRS[self.url] = tempfile.mkdtemp("dvc-cache")
+
+        self.cache.local.cache_dir = cache_dir
+
+    def _set_upstream(self):
+        # check if the URL is local and no default remote is present
+        # add default remote pointing to the original repo's cache location
+        if os.path.isdir(self.url):
+            if not self.config["core"].get("remote"):
+                src_repo = Repo(self.url)
+                try:
+                    cache_dir = src_repo.cache.local.cache_dir
+                finally:
+                    src_repo.close()
+
+                self.config["remote"]["auto-generated-upstream"] = {
+                    "url": cache_dir
+                }
+                self.config["core"]["remote"] = "auto-generated-upstream"
+
+
+class ExternalGitRepo:
+    def __init__(self, root_dir, url):
+        self.root_dir = root_dir
+        self.url = url
+
+    @cached_property
+    def scm(self):
+        return Git(self.root_dir)
+
+    def close(self):
+        if "scm" in self.__dict__:
+            self.scm.close()
+
+    def find_out_by_relpath(self, path):
+        raise OutputNotFoundError(path, self)
+
+    def pull_to(self, path, to_info):
+        try:
+            # Git handled files can't have absolute path
+            if os.path.isabs(path):
+                raise FileNotFoundError
+
+            fs_copy(os.path.join(self.root_dir, path), fspath(to_info))
+        except FileNotFoundError:
+            raise PathMissingError(path, self.url)
+
+    @contextmanager
+    def open_by_relpath(self, path, mode="r", encoding=None, **kwargs):
+        try:
+            abs_path = os.path.join(self.root_dir, path)
+            with open(abs_path, mode, encoding=encoding) as fd:
+                yield fd
+        except FileNotFoundError:
+            raise PathMissingError(path, self.url)
+
+
+def _cached_clone(url, rev, for_write=False):
+    """Clone an external git repo to a temporary directory.
+
+    Returns the path to a local temporary directory with the specified
+    revision checked out. If for_write is set prevents reusing this dir via
+    cache.
+    """
+    if not for_write and Git.is_sha(rev) and (url, rev) in CLONES:
+        return CLONES[url, rev]
+
+    clone_path = _clone_default_branch(url, rev)
+    rev_sha = Git(clone_path).resolve_rev(rev or "HEAD")
+
+    if not for_write and (url, rev_sha) in CLONES:
+        return CLONES[url, rev_sha]
+
+    # Copy to a new dir to keep the clone clean
+    repo_path = tempfile.mkdtemp("dvc-erepo")
+    copy_tree(clone_path, repo_path)
+
+    # Check out the specified revision
+    if rev is not None:
+        _git_checkout(repo_path, rev)
+
+    if not for_write:
+        CLONES[url, rev_sha] = repo_path
+    return repo_path
+
+
+@wrap_with(threading.Lock())
+def _clone_default_branch(url, rev):
+    """Get or create a clean clone of the url.
+
+    The cloned is reactualized with git pull unless rev is a known sha.
+    """
+    clone_path = CLONES.get(url)
+
+    git = None
+    try:
+        if clone_path:
+            git = Git(clone_path)
+            # Do not pull for known shas, branches and tags might move
+            if not Git.is_sha(rev) or not git.has_rev(rev):
+                git.pull()
+        else:
+            clone_path = tempfile.mkdtemp("dvc-clone")
+            git = Git.clone(url, clone_path)
+            CLONES[url] = clone_path
+    finally:
+        if git:
+            git.close()
+
+    return clone_path
+
+
+def _git_checkout(repo_path, rev):
+    git = Git(repo_path)
+    try:
+        git.checkout(rev)
+    finally:
+        git.close()
+
+
 def _remove(path):
    if os.name == "nt":
        # git.exe may hang for a while not permitting to remove temp dir
@@ -123,26 +246,3 @@ def _remove(path):
        os_retry(remove)(path)
    else:
        remove(path)
-
-
-def _clone_repo(url, path):
-    from dvc.scm.git import Git
-
-    git = Git.clone(url, path)
-    git.close()
-
-
-def _default_remote_set(rconfig):
-    """
-    Checks if default remote config is present.
-    Args:
-        rconfig: a remote config
-
-    Returns:
-        True if the default remote config is set, else False
-    """
-    try:
-        rconfig.get_default()
-        return True
-    except ConfigError:
-        return False
@@ -1,11 +1,11 @@
-from __future__ import unicode_literals
-
 import logging
 import os

+from funcy import cached_property
 from pathspec import PathSpec
 from pathspec.patterns import GitWildMatchPattern

+from dvc.scm.tree import BaseTree
 from dvc.utils import relpath

 logger = logging.getLogger(__name__)
@@ -72,13 +72,12 @@ class DvcIgnoreDirs(DvcIgnore):


 class DvcIgnoreFilter(object):
-    def __init__(self, root_dir, tree):
+    def __init__(self, tree):
        self.tree = tree
        self.ignores = {DvcIgnoreDirs([".git", ".hg", ".dvc"])}
-        self._update(root_dir)
-        for root, dirs, _ in self.tree.walk(root_dir, dvcignore=self):
-            for d in dirs:
-                self._update(os.path.join(root, d))
+        for root, dirs, files in self.tree.walk(self.tree.tree_root):
+            self._update(root)
+            dirs[:], files[:] = self(root, dirs, files)

    def _update(self, dirname):
        ignore_file_path = os.path.join(dirname, DvcIgnore.DVCIGNORE_FILE)
@@ -90,3 +89,39 @@ class DvcIgnoreFilter(object):
            dirs, files = ignore(root, dirs, files)

        return dirs, files
+
+
+class CleanTree(BaseTree):
+    def __init__(self, tree):
+        self.tree = tree
+
+    @cached_property
+    def dvcignore(self):
+        return DvcIgnoreFilter(self.tree)
+
+    @property
+    def tree_root(self):
+        return self.tree.tree_root
+
+    def open(self, path, mode="r", encoding="utf-8"):
+        return self.tree.open(path, mode, encoding)
+
+    def exists(self, path):
+        return self.tree.exists(path)
+
+    def isdir(self, path):
+        return self.tree.isdir(path)
+
+    def isfile(self, path):
+        return self.tree.isfile(path)
+
+    def walk(self, top, topdown=True):
+        for root, dirs, files in self.tree.walk(top, topdown):
+            dirs[:], files[:] = self.dvcignore(root, dirs, files)
+
+            yield root, dirs, files
+
+    def walk_files(self, top):
+        for root, _, files in self.walk(top):
+            for file in files:
+                yield os.path.join(root, file)
@@ -1,24 +1,10 @@
 """Use heuristics to guess if it is a text file or a binary file."""
-from __future__ import unicode_literals
-
-from dvc.utils.compat import is_py3
-from dvc.utils.compat import open

 # Based on https://eli.thegreenplace.net/2011/10/19/
 # perls-guess-if-file-is-text-or-binary-implemented-in-python


-# A function that takes an integer in the 8-bit range and returns
-# a single-character byte object in py3 / a single-character string
-# in py2.
-#
-def _int2byte(i):
-    if is_py3:
-        return bytes((i,))
-    return chr(i)
-
-
-TEXT_CHARS = b"".join(_int2byte(i) for i in range(32, 127)) + b"\n\r\t\f\b"
+TEXT_CHARS = bytes(range(32, 127)) + b"\n\r\t\f\b"


 def istextfile(fname, blocksize=512):
@@ -1,5 +1,4 @@
 """Manages dvc lock file."""
-from __future__ import unicode_literals

 import hashlib
 import os
@@ -7,10 +6,10 @@ import time
 from datetime import timedelta

 import zc.lockfile
+import flufl.lock

 from dvc.exceptions import DvcException
 from dvc.utils import format_link
-from dvc.utils.compat import is_py3, is_py2
 from dvc.progress import Tqdm

 DEFAULT_TIMEOUT = 5
@@ -23,11 +22,11 @@ FAILED_TO_LOCK_MESSAGE = (


 class LockError(DvcException):
-    """Thrown when unable to acquire the lock for dvc repo."""
+    """Thrown when unable to acquire the lock for DVC repo."""


 class Lock(object):
-    """Class for dvc repo lock.
+    """Class for DVC repo lock.

    Uses zc.lockfile as backend.
    """
@@ -69,6 +68,10 @@ class Lock(object):
        self._lock.close()
        self._lock = None

+    @property
+    def is_locked(self):
+        return bool(self._lock)
+
    def __enter__(self):
        self.lock()

@@ -76,83 +79,70 @@ class Lock(object):
        self.unlock()


-if is_py3:
-    import flufl.lock
+class HardlinkLock(flufl.lock.Lock):
+    """Class for DVC repo lock.

-    class HardlinkLock(flufl.lock.Lock):
-        """Class for dvc repo lock.
+    Args:
+        lockfile (str): the lock filename
+            in.
+        tmp_dir (str): a directory to store claim files.
+    """

-        Args:
-            lockfile (str): the lock filename
-                in.
-            tmp_dir (str): a directory to store claim files.
-        """
+    def __init__(self, lockfile, tmp_dir=None, **kwargs):
+        import socket

-        def __init__(self, lockfile, tmp_dir=None, **kwargs):
-            import socket
+        self._tmp_dir = tmp_dir

-            self._tmp_dir = tmp_dir
+        # NOTE: this is basically Lock.__init__ copy-paste, except that
+        # instead of using `socket.getfqdn()` we use `socket.gethostname()`
+        # to speed this up. We've seen [1] `getfqdn()` take ~5sec to return
+        # anything, which is way too slow. `gethostname()` is actually a
+        # fallback for `getfqdn()` when it is not able to resolve a
+        # canonical hostname through network. The claimfile that uses
+        # `self._hostname` is still usable, as it uses `pid` and random
+        # number to generate the resulting lock file name, which is unique
+        # enough for our application.
+        #
+        # [1] https://github.com/iterative/dvc/issues/2582
+        self._hostname = socket.gethostname()

-            # NOTE: this is basically Lock.__init__ copy-paste, except that
-            # instead of using `socket.getfqdn()` we use `socket.gethostname()`
-            # to speed this up. We've seen [1] `getfqdn()` take ~5sec to return
-            # anything, which is way too slow. `gethostname()` is actually a
-            # fallback for `getfqdn()` when it is not able to resolve a
-            # canonical hostname through network. The claimfile that uses
-            # `self._hostname` is still usable, as it uses `pid` and random
-            # number to generate the resulting lock file name, which is unique
-            # enough for our application.
-            #
-            # [1] https://github.com/iterative/dvc/issues/2582
-            self._hostname = socket.gethostname()
+        self._lockfile = lockfile
+        self._lifetime = timedelta(days=365)  # Lock for good by default
+        self._separator = flufl.lock.SEP
+        self._set_claimfile()
+        self._owned = True
+        self._retry_errnos = []

-            self._lockfile = lockfile
-            self._lifetime = timedelta(days=365)  # Lock for good by default
-            self._separator = flufl.lock.SEP
-            self._set_claimfile()
-            self._owned = True
-            self._retry_errnos = []
+    @property
+    def lockfile(self):
+        return self._lockfile

-        @property
-        def lockfile(self):
-            return self._lockfile
+    def lock(self):
+        try:
+            super().lock(timedelta(seconds=DEFAULT_TIMEOUT))
+        except flufl.lock.TimeOutError:
+            raise LockError(FAILED_TO_LOCK_MESSAGE)

-        def lock(self):
-            try:
-                super(Lock, self).lock(timedelta(seconds=DEFAULT_TIMEOUT))
-            except flufl.lock.TimeOutError:
-                raise LockError(FAILED_TO_LOCK_MESSAGE)
+    def _set_claimfile(self, pid=None):
+        super()._set_claimfile(pid)

-        def _set_claimfile(self, pid=None):
-            super(Lock, self)._set_claimfile(pid)
+        if self._tmp_dir is not None:
+            # Under Windows file path length is limited so we hash it
+            filename = hashlib.md5(self._claimfile.encode()).hexdigest()
+            self._claimfile = os.path.join(self._tmp_dir, filename + ".lock")

-            if self._tmp_dir is not None:
-                # Under Windows file path length is limited so we hash it
-                filename = hashlib.md5(self._claimfile.encode()).hexdigest()
-                self._claimfile = os.path.join(
-                    self._tmp_dir, filename + ".lock"
-                )
-
-        # Fix for __del__ bug in flufl.lock [1] which is causing errors on
-        # Python shutdown [2].
-        # [1] https://gitlab.com/warsaw/flufl.lock/issues/7
-        # [2] https://github.com/iterative/dvc/issues/2573
-        def __del__(self):
-            try:
-                if self._owned:
-                    self.finalize()
-            except ImportError:
-                pass
+    # Fix for __del__ bug in flufl.lock [1] which is causing errors on
+    # Python shutdown [2].
+    # [1] https://gitlab.com/warsaw/flufl.lock/issues/7
+    # [2] https://github.com/iterative/dvc/issues/2573
+    def __del__(self):
+        try:
+            if self._owned:
+                self.finalize()
+        except ImportError:
+            pass


 def make_lock(lockfile, tmp_dir=None, friendly=False, hardlink_lock=False):
-    if hardlink_lock and is_py2:
-        raise DvcException(
-            "Hardlink locks are not supported on Python <3.5. "
-            "See `hardlink_lock` in {}".format(
-                format_link("man.dvc.org/config#core")
-            )
-        )
-
    cls = HardlinkLock if hardlink_lock else Lock
    return cls(lockfile, tmp_dir=tmp_dir, friendly=friendly)
@@ -1,5 +1,4 @@
-"""Manages logging configuration for dvc repo."""
-from __future__ import unicode_literals
+"""Manages logging configuration for DVC repo."""

 import logging.config
 import logging.handlers
@@ -7,9 +6,6 @@ import logging.handlers
 import colorama

 from dvc.progress import Tqdm
-from dvc.utils.compat import RecursionError
-from dvc.utils.compat import str
-from dvc.utils.compat import StringIO


 FOOTER = (
@@ -26,7 +22,7 @@ FOOTER = (
 class LoggingException(Exception):
    def __init__(self, record):
        msg = "failed to log {}".format(str(record))
-        super(LoggingException, self).__init__(msg)
+        super().__init__(msg)


 class ExcludeErrorsFilter(logging.Filter):
@@ -40,117 +36,69 @@ class ExcludeInfoFilter(logging.Filter):


 class ColorFormatter(logging.Formatter):
-    """Enable color support when logging to a terminal that supports it.
+    """Spit out colored text in supported terminals.

-    Color support on Windows versions that do not support ANSI color codes is
-    enabled by use of the colorama__ library.
+    colorama__ makes ANSI escape character sequences work under Windows.
    See the colorama documentation for details.

    __ https://pypi.python.org/pypi/colorama

-    For records containing `exc_info`, it will use a custom `_walk_exc` to
-    retrieve the whole traceback.
+    If record has an extra `tb_only` attribute, it will not show the
+    exception cause, just the message and the traceback.
    """

    color_code = {
        "DEBUG": colorama.Fore.BLUE,
-        "INFO": "",
        "WARNING": colorama.Fore.YELLOW,
        "ERROR": colorama.Fore.RED,
        "CRITICAL": colorama.Fore.RED,
    }

    def format(self, record):
+        msg = record.msg.format(*record.args) if record.args else record.msg
+
        if record.levelname == "INFO":
-            return record.msg
+            return msg

-        if record.levelname == "ERROR" or record.levelname == "CRITICAL":
-            exception, stack_trace = self._parse_exc(record.exc_info)
+        if record.exc_info:
+            if getattr(record, "tb_only", False):
+                cause = ""
+            else:
+                cause = ": ".join(_iter_causes(record.exc_info[1]))

-            return (
-                "{color}{levelname}{nc}: {description}" "{stack_trace}\n"
-            ).format(
-                color=self.color_code.get(record.levelname, ""),
-                nc=colorama.Fore.RESET,
-                levelname=record.levelname,
-                description=self._description(record.msg, exception),
-                msg=record.msg,
-                stack_trace=stack_trace,
+            msg = "{message}{separator}{cause}".format(
+                message=msg or "",
+                separator=" - " if msg and cause else "",
+                cause=cause,
            )

-        return "{color}{levelname}{nc}: {msg}".format(
-            color=self.color_code.get(record.levelname, ""),
+            if _is_verbose():
+                msg += _stack_trace(record.exc_info)
+
+        return "{asctime}{color}{levelname}{nc}: {msg}".format(
+            asctime=self.formatTime(record, self.datefmt),
+            color=self.color_code[record.levelname],
            nc=colorama.Fore.RESET,
            levelname=record.levelname,
-            msg=record.msg,
+            msg=msg,
        )

-    def _current_level(self):
-        return logging.getLogger("dvc").getEffectiveLevel()
+    def formatTime(self, record, datefmt=None):
+        # only show if current level is set to DEBUG
+        # also, skip INFO as it is used for UI
+        if not _is_verbose() or record.levelno == logging.INFO:
+            return ""

-    def _is_visible(self, record):
-        return record.levelno >= self._current_level()
-
-    def _description(self, message, exception):
-        description = ""
-
-        if exception and message:
-            description = "{message} - {exception}"
-        elif exception:
-            description = "{exception}"
-        elif message:
-            description = "{message}"
-
-        return description.format(message=message, exception=exception)
-
-    def _walk_exc(self, exc_info):
-        import traceback
-
-        buffer = StringIO()
-
-        traceback.print_exception(*exc_info, file=buffer)
-
-        exc = exc_info[1]
-        tb = buffer.getvalue()
-
-        exc_list = [str(exc)]
-        tb_list = [tb]
-
-        # NOTE: parsing chained exceptions. See dvc/exceptions.py for more info
-        while hasattr(exc, "cause") and exc.cause:
-            exc_list.append(str(exc.cause))
-            if hasattr(exc, "cause_tb") and exc.cause_tb:
-                tb_list.insert(0, str(exc.cause_tb))
-            exc = exc.cause
-
-        return exc_list, tb_list
-
-    def _parse_exc(self, exc_info):
-        if not exc_info:
-            return (None, "")
-
-        exc_list, tb_list = self._walk_exc(exc_info)
-
-        exception = ": ".join(exc_list)
-
-        if self._current_level() == logging.DEBUG:
-            stack_trace = (
-                "\n" "{red}{line}{nc}\n" "{stack_trace}" "{red}{line}{nc}"
-            ).format(
-                red=colorama.Fore.RED,
-                nc=colorama.Fore.RESET,
-                line="-" * 60,
-                stack_trace="\n".join(tb_list),
-            )
-        else:
-            stack_trace = ""
-
-        return (exception, stack_trace)
+        return "{green}{date}{nc} ".format(
+            green=colorama.Fore.GREEN,
+            date=super().formatTime(record, datefmt),
+            nc=colorama.Fore.RESET,
+        )


 class LoggerHandler(logging.StreamHandler):
    def handleError(self, record):
-        super(LoggerHandler, self).handleError(record)
+        super().handleError(record)
        raise LoggingException(record)

    def emit(self, record):
@@ -167,6 +115,32 @@ class LoggerHandler(logging.StreamHandler):
            self.handleError(record)


+def _is_verbose():
+    return logging.getLogger("dvc").getEffectiveLevel() == logging.DEBUG
+
+
+def _iter_causes(exc):
+    while exc:
+        yield str(exc)
+        exc = exc.__cause__
+
+
+def _stack_trace(exc_info):
+    import traceback
+
+    return (
+        "\n"
+        "{red}{line}{nc}\n"
+        "{trace}"
+        "{red}{line}{nc}".format(
+            red=colorama.Fore.RED,
+            line="-" * 60,
+            trace="".join(traceback.format_exception(*exc_info)),
+            nc=colorama.Fore.RESET,
+        )
+    )
+
+
 def setup(level=logging.INFO):
    colorama.init()

@@ -1,5 +1,4 @@
 """Main entry point for dvc CLI."""
-from __future__ import unicode_literals

 import errno
 import logging
@@ -11,13 +10,13 @@ from dvc.exceptions import DvcParserError
 from dvc.exceptions import NotDvcRepoError
 from dvc.external_repo import clean_repos
 from dvc.logger import FOOTER
+from dvc.utils import format_link
 from dvc.remote.pool import close_pools
-from dvc.utils.compat import is_py2
-

 # Workaround for CPython bug. See [1] and [2] for more info.
 # [1] https://github.com/aws/aws-cli/blob/1.16.277/awscli/clidriver.py#L55
 # [2] https://bugs.python.org/issue29288
+
 "".encode("idna")


@@ -60,14 +59,14 @@ def main(argv=None):
    except DvcParserError:
        ret = 254
    except Exception as exc:  # pylint: disable=broad-except
-        if isinstance(exc, UnicodeError) and is_py2:
+        if isinstance(exc, OSError) and exc.errno == errno.EMFILE:
            logger.exception(
-                "unicode is not supported in DVC for Python 2 "
-                "(end-of-life January 1, 2020), please upgrade to Python 3"
-            )
-        elif isinstance(exc, OSError) and exc.errno == errno.EMFILE:
-            logger.exception(
-                "too many open files, please increase your `ulimit`"
+                "too many open files, please visit "
+                "{} to see how to handle this "
+                "problem".format(
+                    format_link("https://error.dvc.org/many-files")
+                ),
+                extra={"tb_only": True},
            )
        else:
            logger.exception("unexpected error")
@@ -75,8 +74,9 @@ def main(argv=None):
    finally:
        logger.setLevel(outerLogLevel)

-        # Python 2 fails to close these clean occasionally and users see
-        # weird error messages, so we do it manually
+        # Closing pools by-hand to prevent wierd messages when closing SSH
+        # connections. See https://github.com/iterative/dvc/issues/3248 for
+        # more info.
        close_pools()

        # Remove cached repos in the end of the call, these are anonymous
@@ -1,6 +1,5 @@
-from __future__ import unicode_literals
-
-from voluptuous import Any, Required
+from urllib.parse import urlparse
+from voluptuous import Any, Required, Lower, Length, Coerce, And, SetTo

 from dvc.output.base import OutputBase
 from dvc.output.gs import OutputGS
@@ -13,8 +12,6 @@ from dvc.remote.hdfs import RemoteHDFS
 from dvc.remote.local import RemoteLOCAL
 from dvc.remote.s3 import RemoteS3
 from dvc.scheme import Schemes
-from dvc.utils.compat import str
-from dvc.utils.compat import urlparse

 OUTS = [
    OutputHDFS,
@@ -32,6 +29,12 @@ OUTS_MAP = {
    Schemes.LOCAL: OutputLOCAL,
 }

+CHECKSUM_SCHEMA = Any(
+    None,
+    And(str, Length(max=0), SetTo(None)),
+    And(Any(str, And(int, Coerce(str))), Length(min=3), Lower),
+)
+
 # NOTE: currently there are only 3 possible checksum names:
 #
 #    1) md5 (LOCAL, SSH, GS);
@@ -40,15 +43,15 @@ OUTS_MAP = {
 #
 # so when a few types of outputs share the same name, we only need
 # specify it once.
-CHECKSUM_SCHEMA = {
-    RemoteLOCAL.PARAM_CHECKSUM: Any(str, None),
-    RemoteS3.PARAM_CHECKSUM: Any(str, None),
-    RemoteHDFS.PARAM_CHECKSUM: Any(str, None),
+CHECKSUMS_SCHEMA = {
+    RemoteLOCAL.PARAM_CHECKSUM: CHECKSUM_SCHEMA,
+    RemoteS3.PARAM_CHECKSUM: CHECKSUM_SCHEMA,
+    RemoteHDFS.PARAM_CHECKSUM: CHECKSUM_SCHEMA,
 }

-TAGS_SCHEMA = {str: CHECKSUM_SCHEMA}
+TAGS_SCHEMA = {str: CHECKSUMS_SCHEMA}

-SCHEMA = CHECKSUM_SCHEMA.copy()
+SCHEMA = CHECKSUMS_SCHEMA.copy()
 SCHEMA[Required(OutputBase.PARAM_PATH)] = str
 SCHEMA[OutputBase.PARAM_CACHE] = bool
 SCHEMA[OutputBase.PARAM_METRIC] = OutputBase.METRIC_SCHEMA
@@ -1,17 +1,14 @@
-from __future__ import unicode_literals
-
 import logging
+from urllib.parse import urlparse
 from copy import copy

 from voluptuous import Any

 import dvc.prompt as prompt
 from dvc.cache import NamedCache
-from dvc.exceptions import CollectCacheError
+from dvc.exceptions import CollectCacheError, RemoteCacheRequiredError
 from dvc.exceptions import DvcException
 from dvc.remote.base import RemoteBASE
-from dvc.utils.compat import str
-from dvc.utils.compat import urlparse


 logger = logging.getLogger(__name__)
@@ -20,26 +17,24 @@ logger = logging.getLogger(__name__)
 class OutputDoesNotExistError(DvcException):
    def __init__(self, path):
        msg = "output '{}' does not exist".format(path)
-        super(OutputDoesNotExistError, self).__init__(msg)
+        super().__init__(msg)


 class OutputIsNotFileOrDirError(DvcException):
    def __init__(self, path):
        msg = "output '{}' is not a file or directory".format(path)
-        super(OutputIsNotFileOrDirError, self).__init__(msg)
+        super().__init__(msg)


 class OutputAlreadyTrackedError(DvcException):
    def __init__(self, path):
        msg = "output '{}' is already tracked by scm (e.g. git)".format(path)
-        super(OutputAlreadyTrackedError, self).__init__(msg)
+        super().__init__(msg)


 class OutputIsStageFileError(DvcException):
    def __init__(self, path):
-        super(OutputIsStageFileError, self).__init__(
-            "Stage file '{}' cannot be an output.".format(path)
-        )
+        super().__init__("Stage file '{}' cannot be an output.".format(path))


 class OutputBase(object):
@@ -103,14 +98,9 @@ class OutputBase(object):
        self.persist = persist
        self.tags = None if self.IS_DEPENDENCY else (tags or {})

-        if self.use_cache and self.cache is None:
-            raise DvcException(
-                "no cache location setup for '{}' outputs.".format(
-                    self.REMOTE.scheme
-                )
-            )
-
        self.path_info = self._parse_path(remote, path)
+        if self.use_cache and self.cache is None:
+            raise RemoteCacheRequiredError(self.path_info)

    def _parse_path(self, remote, path):
        if remote:
@@ -172,11 +162,11 @@ class OutputBase(object):
    def changed_checksum(self):
        return self.checksum != self.remote.get_checksum(self.path_info)

-    def changed_cache(self):
+    def changed_cache(self, filter_info=None):
        if not self.use_cache or not self.checksum:
            return True

-        return self.cache.changed_cache(self.checksum)
+        return self.cache.changed_cache(self.checksum, filter_info=filter_info)

    def status(self):
        if self.checksum and self.use_cache and self.changed_cache():
@@ -283,11 +273,18 @@ class OutputBase(object):
        self.remote.download(self.path_info, to.path_info)

    def checkout(
-        self, force=False, progress_callback=None, tag=None, relink=False
+        self,
+        force=False,
+        progress_callback=None,
+        tag=None,
+        relink=False,
+        filter_info=None,
    ):
        if not self.use_cache:
            if progress_callback:
-                progress_callback(str(self.path_info), self.get_files_number())
+                progress_callback(
+                    str(self.path_info), self.get_files_number(filter_info)
+                )
            return None

        if tag:
@@ -301,6 +298,7 @@ class OutputBase(object):
            force=force,
            progress_callback=progress_callback,
            relink=relink,
+            filter_info=filter_info,
        )

    def remove(self, ignore_remove=False):
@@ -324,17 +322,21 @@ class OutputBase(object):
        if self.scheme == "local" and self.use_scm_ignore:
            self.repo.scm.ignore(self.fspath)

-    def get_files_number(self):
+    def get_files_number(self, filter_info=None):
        if not self.use_cache:
            return 0

-        return self.cache.get_files_number(self.checksum)
+        return self.cache.get_files_number(
+            self.path_info, self.checksum, filter_info
+        )

    def unprotect(self):
        if self.exists:
            self.remote.unprotect(self.path_info)

-    def _collect_used_dir_cache(self, remote=None, force=False, jobs=None):
+    def _collect_used_dir_cache(
+        self, remote=None, force=False, jobs=None, filter_info=None
+    ):
        """Get a list of `info`s related to the given directory.

        - Pull the directory entry from the remote cache if it was changed.
@@ -383,8 +385,9 @@ class OutputBase(object):

        for entry in self.dir_cache:
            checksum = entry[self.remote.PARAM_CHECKSUM]
-            path_info = self.path_info / entry[self.remote.PARAM_RELPATH]
-            cache.add(self.scheme, checksum, str(path_info))
+            info = self.path_info / entry[self.remote.PARAM_RELPATH]
+            if not filter_info or info.isin_or_eq(filter_info):
+                cache.add(self.scheme, checksum, str(info))

        return cache

@@ -400,10 +403,16 @@ class OutputBase(object):
        if not self.use_cache:
            return NamedCache()

+        if self.stage.is_repo_import:
+            cache = NamedCache()
+            (dep,) = self.stage.deps
+            cache.external[dep.repo_pair].add(dep.def_path)
+            return cache
+
        if not self.info:
            logger.warning(
                "Output '{}'({}) is missing version info. Cache for it will "
-                "not be collected. Use dvc repro to get your pipeline up to "
+                "not be collected. Use `dvc repro` to get your pipeline up to "
                "date.".format(self, self.stage)
            )
            return NamedCache()
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.output.s3 import OutputS3
 from dvc.remote.gs import RemoteGS

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.output.base import OutputBase
 from dvc.remote.hdfs import RemoteHDFS

@@ -1,16 +1,13 @@
-from __future__ import unicode_literals
-
 import logging
 import os
+from urllib.parse import urlparse

 from dvc.exceptions import DvcException
 from dvc.istextfile import istextfile
 from dvc.output.base import OutputBase
 from dvc.remote.local import RemoteLOCAL
 from dvc.utils import relpath
-from dvc.utils.compat import fspath_py35
-from dvc.utils.compat import str
-from dvc.utils.compat import urlparse
+from dvc.compat import fspath_py35
 from dvc.utils.fs import path_isin


@@ -21,6 +18,12 @@ class OutputLOCAL(OutputBase):
    REMOTE = RemoteLOCAL
    sep = os.sep

+    def __init__(self, stage, path, *args, **kwargs):
+        if stage and path_isin(path, stage.repo.root_dir):
+            path = relpath(path, stage.wdir)
+
+        super().__init__(stage, path, *args, **kwargs)
+
    def _parse_path(self, remote, path):
        parsed = urlparse(path)
        if parsed.scheme == "remote":
@@ -59,7 +62,7 @@ class OutputLOCAL(OutputBase):
        return def_scheme != "remote" and not os.path.isabs(self.def_path)

    def dumpd(self):
-        ret = super(OutputLOCAL, self).dumpd()
+        ret = super().dumpd()
        if self.is_in_repo:
            path = self.path_info.relpath(self.stage.wdir).as_posix()
        else:
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.output.base import OutputBase
 from dvc.remote.s3 import RemoteS3

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from dvc.output.base import OutputBase
 from dvc.remote.ssh import RemoteSSH

@@ -1,35 +1,23 @@
-from __future__ import absolute_import
-from __future__ import unicode_literals
-
 import os
 import posixpath
-import sys
+import pathlib
+from urllib.parse import urlparse

 from funcy import cached_property

 from dvc.utils import relpath
-from dvc.utils.compat import basestring
-from dvc.utils.compat import builtin_str
-from dvc.utils.compat import is_py2
-from dvc.utils.compat import pathlib
-from dvc.utils.compat import str
-from dvc.utils.compat import urlparse
-
-
-# On Python 2.7/Windows sys.getfilesystemencoding() is set to mbcs,
-# which is lossy, thus we can't use that,
-# see https://github.com/mcmtroffaes/pathlib2/issues/56.
-if is_py2:
-    fs_encoding = "utf-8"


 class _BasePath(object):
    def overlaps(self, other):
-        if isinstance(other, basestring):
+        if isinstance(other, (str, bytes)):
            other = self.__class__(other)
        elif self.__class__ != other.__class__:
            return False
-        return self == other or self.isin(other) or other.isin(self)
+        return self.isin_or_eq(other) or other.isin(self)
+
+    def isin_or_eq(self, other):
+        return self == other or self.isin(other)


 class PathInfo(pathlib.PurePath, _BasePath):
@@ -63,7 +51,7 @@ class PathInfo(pathlib.PurePath, _BasePath):
        return relpath(path)

    def __repr__(self):
-        return builtin_str("{}: '{}'").format(type(self).__name__, self)
+        return "{}: '{}'".format(type(self).__name__, self)

    # This permits passing it to file utils directly in Python 3.6+
    # With Python 2.7, Python 3.5+ we are stuck with path_info.fspath for now
@@ -80,7 +68,7 @@ class PathInfo(pathlib.PurePath, _BasePath):
        return self.__class__(relpath(self, other))

    def isin(self, other):
-        if isinstance(other, basestring):
+        if isinstance(other, (str, bytes)):
            other = self.__class__(other)
        elif self.__class__ != other.__class__:
            return False
@@ -88,34 +76,6 @@ class PathInfo(pathlib.PurePath, _BasePath):
        n = len(other._cparts)
        return len(self._cparts) > n and self._cparts[:n] == other._cparts

-    # pathlib2 uses bytes internally in Python 2, and we use unicode everywhere
-    # for paths in both pythons, thus we need this glue.
-    if is_py2:
-        __unicode__ = __str__
-
-        def __str__(self):
-            return self.__unicode__().encode(sys.getfilesystemencoding())
-
-        @classmethod
-        def _parse_args(cls, args):
-            args = [
-                a.encode(fs_encoding)
-                if isinstance(a, unicode)  # noqa: F821
-                else a
-                for a in args
-            ]
-            return super(PathInfo, cls)._parse_args(args)
-
-        @property
-        def name(self):
-            return super(PathInfo, self).name.decode(fs_encoding)
-
-        def __fspath__(self):  # noqa: F811
-            return pathlib.PurePath.__str__(self).decode(fs_encoding)
-
-        def with_name(self, name):
-            return pathlib.PurePath.with_name(self, name.encode(fs_encoding))
-

 class WindowsPathInfo(PathInfo, pathlib.PureWindowsPath):
    pass
@@ -172,13 +132,13 @@ class URLInfo(_BasePath):

    def fill_parts(self, scheme, host, user, port, path):
        assert scheme != "remote"
-        assert isinstance(path, (basestring, _URLPathInfo))
+        assert isinstance(path, (str, bytes, _URLPathInfo))

        self.scheme, self.host, self.user = scheme, host, user
        self.port = int(port) if port else self.DEFAULT_PORTS.get(self.scheme)

        if isinstance(path, _URLPathInfo):
-            self._spath = builtin_str(path)
+            self._spath = str(path)
            self._path = path
        else:
            if path and path[0] != "/":
@@ -207,7 +167,7 @@ class URLInfo(_BasePath):
        return "{}: '{}'".format(type(self).__name__, self)

    def __eq__(self, other):
-        if isinstance(other, basestring):
+        if isinstance(other, (str, bytes)):
            other = self.__class__(other)
        return (
            self.__class__ == other.__class__
@@ -257,7 +217,7 @@ class URLInfo(_BasePath):
        return _URLPathParents(self)

    def relative_to(self, other):
-        if isinstance(other, basestring):
+        if isinstance(other, (str, bytes)):
            other = self.__class__(other)
        if self.__class__ != other.__class__:
            msg = "'{}' has incompatible class with '{}'".format(self, other)
@@ -268,7 +228,7 @@ class URLInfo(_BasePath):
        return self._path.relative_to(other._path)

    def isin(self, other):
-        if isinstance(other, basestring):
+        if isinstance(other, (str, bytes)):
            other = self.__class__(other)
        elif self.__class__ != other.__class__:
            return False
@@ -1,11 +1,9 @@
-"""Manages progress bars for dvc repo."""
-from __future__ import print_function
+"""Manages progress bars for DVC repo."""

 import logging
 import sys
 from threading import RLock

-from funcy import merge
 from tqdm import tqdm

 from dvc.utils import env2bool
@@ -32,7 +30,10 @@ class Tqdm(tqdm):
    )
    BAR_FMT_NOTOTAL = (
        "{desc:{ncols_desc}.{ncols_desc}}{n_fmt}"
-        " [{elapsed}<??:??, {rate_fmt:>11}{postfix}]"
+        " [{elapsed}, {rate_fmt:>11}{postfix}]"
+    )
+    BYTES_DEFAULTS = dict(
+        unit="B", unit_scale=True, unit_divisor=1024, miniters=1
    )

    def __init__(
@@ -45,6 +46,7 @@ class Tqdm(tqdm):
        bar_format=None,
        bytes=False,  # pylint: disable=W0622
        file=None,
+        total=None,
        **kwargs
    ):
        """
@@ -53,23 +55,22 @@ class Tqdm(tqdm):
        desc  : persists after `close()`
        level  : effective logging level for determining `disable`;
            used only if `disable` is unspecified
-        disable  : If (default: None), will be determined by logging level.
+        disable  : If (default: None) or False,
+            will be determined by logging level.
            May be overridden to `True` due to non-TTY status.
            Skip override by specifying env var `DVC_IGNORE_ISATTY`.
        kwargs  : anything accepted by `tqdm.tqdm()`
        """
        kwargs = kwargs.copy()
-        kwargs.setdefault("unit_scale", True)
        if bytes:
-            bytes_defaults = dict(
-                unit="B", unit_scale=True, unit_divisor=1024, miniters=1
-            )
-            kwargs = merge(bytes_defaults, kwargs)
+            kwargs = {**self.BYTES_DEFAULTS, **kwargs}
+        else:
+            kwargs.setdefault("unit_scale", total > 999 if total else True)
        if file is None:
            file = sys.stderr
        self.desc_persist = desc
        # auto-disable based on `logger.level`
-        if disable is None:
+        if not disable:
            disable = logger.getEffectiveLevel() > level
        # auto-disable based on TTY
        if (
@@ -78,13 +79,14 @@ class Tqdm(tqdm):
            and hasattr(file, "isatty")
        ):
            disable = not file.isatty()
-        super(Tqdm, self).__init__(
+        super().__init__(
            iterable=iterable,
            disable=disable,
            leave=leave,
            desc=desc,
            bar_format="!",
            lock_args=(False,),
+            total=total,
            **kwargs
        )
        if bar_format is None:
@@ -115,12 +117,16 @@ class Tqdm(tqdm):
    def close(self):
        if self.desc_persist is not None:
            self.set_description_str(self.desc_persist, refresh=False)
-        super(Tqdm, self).close()
+        # unknown/zero ETA
+        self.bar_format = self.bar_format.replace("<{remaining}", "")
+        # remove completed bar
+        self.bar_format = self.bar_format.replace("|{bar:10}|", " ")
+        super().close()

    @property
    def format_dict(self):
        """inject `ncols_desc` to fill the display width (`ncols`)"""
-        d = super(Tqdm, self).format_dict
+        d = super().format_dict
        ncols = d["ncols"] or 80
        ncols_desc = ncols - len(self.format_meter(ncols_desc=1, **d)) + 1
        ncols_desc = max(ncols_desc, 0)
@@ -1,14 +1,9 @@
 """Manages user prompts."""
-from __future__ import print_function
-from __future__ import unicode_literals

 import logging
 import sys
 from getpass import getpass

-from dvc.utils.compat import input
-
-
 logger = logging.getLogger(__name__)


@@ -1,6 +1,6 @@
-from __future__ import unicode_literals
+import posixpath
+from urllib.parse import urlparse

-from .config import RemoteConfig
 from dvc.remote.azure import RemoteAZURE
 from dvc.remote.gdrive import RemoteGDrive
 from dvc.remote.gs import RemoteGS
@@ -27,9 +27,9 @@ REMOTES = [
 ]


-def _get(config):
+def _get(remote_conf):
    for remote in REMOTES:
-        if remote.supported(config):
+        if remote.supported(remote_conf):
            return remote
    return RemoteLOCAL

@@ -37,8 +37,39 @@ def _get(config):
 def Remote(repo, **kwargs):
    name = kwargs.get("name")
    if name:
-        remote_config = RemoteConfig(repo.config)
-        settings = remote_config.get_settings(name)
+        remote_conf = repo.config["remote"][name.lower()]
    else:
-        settings = kwargs
-    return _get(settings)(repo, settings)
+        remote_conf = kwargs
+    remote_conf = _resolve_remote_refs(repo.config, remote_conf)
+    return _get(remote_conf)(repo, remote_conf)
+
+
+def _resolve_remote_refs(config, remote_conf):
+    # Support for cross referenced remotes.
+    # This will merge the settings, shadowing base ref with remote_conf.
+    # For example, having:
+    #
+    #       dvc remote add server ssh://localhost
+    #       dvc remote modify server user root
+    #       dvc remote modify server ask_password true
+    #
+    #       dvc remote add images remote://server/tmp/pictures
+    #       dvc remote modify images user alice
+    #       dvc remote modify images ask_password false
+    #       dvc remote modify images password asdf1234
+    #
+    # Results on a config dictionary like:
+    #
+    #       {
+    #           "url": "ssh://localhost/tmp/pictures",
+    #           "user": "alice",
+    #           "password": "asdf1234",
+    #           "ask_password": False,
+    #       }
+    parsed = urlparse(remote_conf["url"])
+    if parsed.scheme != "remote":
+        return remote_conf
+
+    base = config["remote"][parsed.netloc]
+    url = posixpath.join(base["url"], parsed.path.lstrip("/"))
+    return {**base, **remote_conf, "url": url}
@@ -1,20 +1,16 @@
-from __future__ import absolute_import
-from __future__ import unicode_literals
-
 import logging
 import os
 import re
 from datetime import datetime, timedelta
+from urllib.parse import urlparse
 import threading

 from funcy import cached_property, wrap_prop

-from dvc.config import Config
 from dvc.path_info import CloudURLInfo
 from dvc.progress import Tqdm
 from dvc.remote.base import RemoteBASE
 from dvc.scheme import Schemes
-from dvc.utils.compat import urlparse


 logger = logging.getLogger(__name__)
@@ -34,9 +30,9 @@ class RemoteAZURE(RemoteBASE):
    COPY_POLL_SECONDS = 5

    def __init__(self, repo, config):
-        super(RemoteAZURE, self).__init__(repo, config)
+        super().__init__(repo, config)

-        url = config.get(Config.SECTION_REMOTE_URL, "azure://")
+        url = config.get("url", "azure://")

        match = re.match(self.REGEX, url)  # backward compatibility
        path = match.group("path")
@@ -47,7 +43,7 @@ class RemoteAZURE(RemoteBASE):
        )

        self.connection_string = (
-            config.get(Config.SECTION_AZURE_CONNECTION_STRING)
+            config.get("connection_string")
            or match.group("connection_string")  # backward compatibility
            or os.getenv("AZURE_STORAGE_CONNECTION_STRING")
        )
@@ -1,13 +1,9 @@
-from __future__ import unicode_literals
-
 import errno
-
-from dvc.utils.compat import basestring, FileNotFoundError, str, urlparse
-
 import itertools
 import json
 import logging
 import tempfile
+from urllib.parse import urlparse
 from concurrent.futures import ThreadPoolExecutor
 from copy import copy
 from functools import partial
@@ -17,19 +13,19 @@ from operator import itemgetter
 from shortuuid import uuid

 import dvc.prompt as prompt
-from dvc.config import Config
 from dvc.exceptions import (
    DvcException,
    ConfirmRemoveError,
    DvcIgnoreInCollectedDirError,
+    RemoteCacheRequiredError,
 )
 from dvc.ignore import DvcIgnore
 from dvc.path_info import PathInfo, URLInfo
 from dvc.progress import Tqdm
 from dvc.remote.slow_link_detection import slow_link_guard
 from dvc.state import StateNoop
-from dvc.utils import makedirs, relpath, tmp_fname
-from dvc.utils.fs import move
+from dvc.utils import tmp_fname
+from dvc.utils.fs import move, makedirs
 from dvc.utils.http import open_url

 logger = logging.getLogger(__name__)
@@ -50,7 +46,7 @@ STATUS_MAP = {

 class RemoteCmdError(DvcException):
    def __init__(self, remote, cmd, ret, err):
-        super(RemoteCmdError, self).__init__(
+        super().__init__(
            "{remote} command '{cmd}' finished with non-zero return code"
            " {ret}': {err}".format(remote=remote, cmd=cmd, ret=ret, err=err)
        )
@@ -59,7 +55,7 @@ class RemoteCmdError(DvcException):
 class RemoteActionNotImplemented(DvcException):
    def __init__(self, action, scheme):
        m = "{} is not supported for {} remotes".format(action, scheme)
-        super(RemoteActionNotImplemented, self).__init__(m)
+        super().__init__(m)


 class RemoteMissingDepsError(DvcException):
@@ -67,10 +63,9 @@ class RemoteMissingDepsError(DvcException):


 class DirCacheError(DvcException):
-    def __init__(self, checksum, cause=None):
-        super(DirCacheError, self).__init__(
-            "Failed to load dir cache for checksum: '{}'.".format(checksum),
-            cause=cause,
+    def __init__(self, checksum):
+        super().__init__(
+            "Failed to load dir cache for hash value: '{}'.".format(checksum)
        )


@@ -84,6 +79,8 @@ class RemoteBASE(object):
    CHECKSUM_DIR_SUFFIX = ".dir"
    CHECKSUM_JOBS = max(1, min(4, cpu_count() // 2))
    DEFAULT_CACHE_TYPES = ["copy"]
+    DEFAULT_NO_TRAVERSE = True
+    DEFAULT_VERIFY = False

    state = StateNoop()

@@ -92,22 +89,17 @@ class RemoteBASE(object):

        self._check_requires(config)

-        core = config.get(Config.SECTION_CORE, {})
-        self.checksum_jobs = core.get(
-            Config.SECTION_CORE_CHECKSUM_JOBS, self.CHECKSUM_JOBS
+        self.checksum_jobs = (
+            config.get("checksum_jobs")
+            or (self.repo and self.repo.config["core"].get("checksum_jobs"))
+            or self.CHECKSUM_JOBS
        )
-
        self.protected = False
-        self.no_traverse = config.get(Config.SECTION_REMOTE_NO_TRAVERSE, True)
+        self.no_traverse = config.get("no_traverse", self.DEFAULT_NO_TRAVERSE)
+        self.verify = config.get("verify", self.DEFAULT_VERIFY)
        self._dir_info = {}

-        types = config.get(Config.SECTION_CACHE_TYPE, None)
-        if types:
-            if isinstance(types, str):
-                types = [t.strip() for t in types.split(",")]
-            self.cache_types = types
-        else:
-            self.cache_types = copy(self.DEFAULT_CACHE_TYPES)
+        self.cache_types = config.get("type") or copy(self.DEFAULT_CACHE_TYPES)
        self.cache_type_confirmed = False

    def _check_requires(self, config):
@@ -124,9 +116,7 @@ class RemoteBASE(object):
        if not missing:
            return

-        url = config.get(
-            Config.SECTION_REMOTE_URL, "{}://".format(self.scheme)
-        )
+        url = config.get("url", "{}://".format(self.scheme))
        msg = (
            "URL '{}' is supported but requires these missing "
            "dependencies: {}. If you have installed dvc using pip, "
@@ -155,10 +145,10 @@ class RemoteBASE(object):

    @classmethod
    def supported(cls, config):
-        if isinstance(config, basestring):
+        if isinstance(config, (str, bytes)):
            url = config
        else:
-            url = config[Config.SECTION_REMOTE_URL]
+            url = config["url"]

        # NOTE: silently skipping remote, calling code should handle that
        parsed = urlparse(url)
@@ -179,7 +169,7 @@ class RemoteBASE(object):
                tasks,
                total=len(file_infos),
                unit="md5",
-                desc="Computing hashes (only done once)",
+                desc="Computing file/dir hashes (only done once)",
            ) as tasks:
                checksums = dict(zip(file_infos, tasks))
        return checksums
@@ -222,6 +212,9 @@ class RemoteBASE(object):
        return sorted(result, key=itemgetter(self.PARAM_RELPATH))

    def get_dir_checksum(self, path_info):
+        if not self.cache:
+            raise RemoteCacheRequiredError(path_info)
+
        dir_info = self._collect_dir(path_info)
        checksum, tmp_info = self._get_dir_info_checksum(dir_info)
        new_info = self.cache.checksum_to_path_info(checksum)
@@ -268,11 +261,13 @@ class RemoteBASE(object):
            with self.cache.open(path_info, "r") as fobj:
                d = json.load(fobj)
        except (ValueError, FileNotFoundError) as exc:
-            raise DirCacheError(checksum, cause=exc)
+            raise DirCacheError(checksum) from exc

        if not isinstance(d, list):
-            msg = "dir cache file format error '{}' [skipping the file]"
-            logger.error(msg.format(relpath(path_info)))
+            logger.error(
+                "dir cache file format error '{}' [skipping the file]",
+                path_info,
+            )
            return []

        for info in d:
@@ -325,49 +320,48 @@ class RemoteBASE(object):

        A file is considered changed if:
            - It doesn't exist on the working directory (was unlinked)
-            - Checksum is not computed (saving a new file)
-            - The checkusm stored in the State is different from the given one
+            - Hash value is not computed (saving a new file)
+            - The hash value stored is different from the given one
            - There's no file in the cache

        Args:
            path_info: dict with path information.
-            checksum: expected checksum for this data.
+            checksum: expected hash value for this data.

        Returns:
            bool: True if data has changed, False otherwise.
        """

        logger.debug(
-            "checking if '{}'('{}') has changed.".format(
-                path_info, checksum_info
-            )
+            "checking if '{}'('{}') has changed.", path_info, checksum_info
        )

        if not self.exists(path_info):
-            logger.debug("'{}' doesn't exist.".format(path_info))
+            logger.debug("'{}' doesn't exist.", path_info)
            return True

        checksum = checksum_info.get(self.PARAM_CHECKSUM)
        if checksum is None:
-            logger.debug("checksum for '{}' is missing.".format(path_info))
+            logger.debug("hash value for '{}' is missing.", path_info)
            return True

        if self.changed_cache(checksum):
            logger.debug(
-                "cache for '{}'('{}') has changed.".format(path_info, checksum)
+                "cache for '{}'('{}') has changed.", path_info, checksum
            )
            return True

        actual = self.get_checksum(path_info)
        if checksum != actual:
            logger.debug(
-                "checksum '{}'(actual '{}') for '{}' has changed.".format(
-                    checksum, actual, path_info
-                )
+                "hash value '{}' for '{}' has changed (actual '{}').",
+                checksum,
+                actual,
+                path_info,
            )
            return True

-        logger.debug("'{}' hasn't changed.".format(path_info))
+        logger.debug("'{}' hasn't changed.", path_info)
        return False

    def link(self, from_info, to_info):
@@ -380,18 +374,30 @@ class RemoteBASE(object):

        self._try_links(from_info, to_info, link_types)

+    def _verify_link(self, path_info, link_type):
+        if self.cache_type_confirmed:
+            return
+
+        is_link = getattr(self, "is_{}".format(link_type), None)
+        if is_link and not is_link(path_info):
+            self.remove(path_info)
+            raise DvcException("failed to verify {}".format(link_type))
+
+        self.cache_type_confirmed = True
+
    @slow_link_guard
    def _try_links(self, from_info, to_info, link_types):
        while link_types:
            link_method = getattr(self, link_types[0])
            try:
                self._do_link(from_info, to_info, link_method)
-                self.cache_type_confirmed = True
+                self._verify_link(to_info, link_types[0])
                return

            except DvcException as exc:
-                msg = "Cache type '{}' is not supported: {}"
-                logger.debug(msg.format(link_types[0], str(exc)))
+                logger.debug(
+                    "Cache type '{}' is not supported: {}", link_types[0], exc
+                )
                del link_types[0]

        raise DvcException("no possible cache types left to try out.")
@@ -405,13 +411,13 @@ class RemoteBASE(object):
        if self.protected:
            self.protect(to_info)

-        msg = "Created {}'{}': {} -> {}".format(
+        logger.debug(
+            "Created {}'{}': {} -> {}",
            "protected " if self.protected else "",
            self.cache_types[0],
            from_info,
            to_info,
        )
-        logger.debug(msg)

    def _save_file(self, path_info, checksum, save_link=True):
        assert checksum
@@ -465,7 +471,9 @@ class RemoteBASE(object):
        cache_info = self.checksum_to_path_info(checksum)
        dir_info = self.get_dir_cache(checksum)

-        for entry in dir_info:
+        for entry in Tqdm(
+            dir_info, desc="Saving " + path_info.name, unit="file"
+        ):
            entry_info = path_info / entry[self.PARAM_RELPATH]
            entry_checksum = entry[self.PARAM_CHECKSUM]
            self._save_file(entry_info, entry_checksum, save_link=False)
@@ -513,7 +521,7 @@ class RemoteBASE(object):

    def _save(self, path_info, checksum):
        to_info = self.checksum_to_path_info(checksum)
-        logger.debug("Saving '{}' to '{}'.".format(path_info, to_info))
+        logger.debug("Saving '{}' to '{}'.", path_info, to_info)
        if self.isdir(path_info):
            self._save_dir(path_info, checksum)
            return
@@ -525,8 +533,9 @@ class RemoteBASE(object):
        if isinstance(exception, OSError) and exception.errno == errno.EMFILE:
            raise exception

-        msg = "failed to {} '{}' to '{}'".format(operation, from_info, to_info)
-        logger.exception(msg)
+        logger.exception(
+            "failed to {} '{}' to '{}'", operation, from_info, to_info
+        )
        return 1

    def upload(self, from_info, to_info, name=None, no_progress_bar=False):
@@ -539,7 +548,7 @@ class RemoteBASE(object):
        if from_info.scheme != "local":
            raise NotImplementedError

-        logger.debug("Uploading '{}' to '{}'".format(from_info, to_info))
+        logger.debug("Uploading '{}' to '{}'", from_info, to_info)

        name = name or from_info.name

@@ -618,7 +627,7 @@ class RemoteBASE(object):
    ):
        makedirs(to_info.parent, exist_ok=True, mode=dir_mode)

-        logger.debug("Downloading '{}' to '{}'".format(from_info, to_info))
+        logger.debug("Downloading '{}' to '{}'", from_info, to_info)
        name = name or to_info.name

        tmp_file = tmp_fname(to_info)
@@ -702,6 +711,8 @@ class RemoteBASE(object):
            if checksum in used:
                continue
            path_info = self.checksum_to_path_info(checksum)
+            if self.is_dir_checksum(checksum):
+                self._remove_unpacked_dir(checksum)
            self.remove(path_info)
            removed = True
        return removed
@@ -722,9 +733,10 @@ class RemoteBASE(object):
        actual = self.get_checksum(cache_info)

        logger.debug(
-            "cache '{}' expected '{}' actual '{}'".format(
-                str(cache_info), checksum, actual
-            )
+            "cache '{}' expected '{}' actual '{}'",
+            cache_info,
+            checksum,
+            actual,
        )

        if not checksum or not actual:
@@ -734,29 +746,41 @@ class RemoteBASE(object):
            return False

        if self.exists(cache_info):
-            logger.warning("corrupted cache file '{}'.".format(cache_info))
+            logger.warning("corrupted cache file '{}'.", cache_info)
            self.remove(cache_info)

        return True

-    def _changed_dir_cache(self, checksum):
+    def _changed_dir_cache(self, checksum, path_info=None, filter_info=None):
        if self.changed_cache_file(checksum):
            return True

-        if not self._changed_unpacked_dir(checksum):
+        if not (path_info and filter_info) and not self._changed_unpacked_dir(
+            checksum
+        ):
            return False

        for entry in self.get_dir_cache(checksum):
            entry_checksum = entry[self.PARAM_CHECKSUM]
+
+            if path_info and filter_info:
+                entry_info = path_info / entry[self.PARAM_RELPATH]
+                if not entry_info.isin_or_eq(filter_info):
+                    continue
+
            if self.changed_cache_file(entry_checksum):
                return True

-        self._update_unpacked_dir(checksum)
+        if not (path_info and filter_info):
+            self._update_unpacked_dir(checksum)
+
        return False

-    def changed_cache(self, checksum):
+    def changed_cache(self, checksum, path_info=None, filter_info=None):
        if self.is_dir_checksum(checksum):
-            return self._changed_dir_cache(checksum)
+            return self._changed_dir_cache(
+                checksum, path_info=path_info, filter_info=filter_info
+            )
        return self.changed_cache_file(checksum)

    def cache_exists(self, checksums, jobs=None, name=None):
@@ -832,8 +856,7 @@ class RemoteBASE(object):
        """The file is changed we need to checkout a new copy"""
        cache_info = self.checksum_to_path_info(checksum)
        if self.exists(path_info):
-            msg = "data '{}' exists. Removing before checkout."
-            logger.warning(msg.format(str(path_info)))
+            logger.debug("data '{}' will be replaced.", path_info)
            self.safe_remove(path_info, force=force)

        self.link(cache_info, path_info)
@@ -846,10 +869,15 @@ class RemoteBASE(object):
        """Optional: Implement only if the remote needs to create
        directories before copying/linking/moving data
        """
-        pass

    def _checkout_dir(
-        self, path_info, checksum, force, progress_callback=None, relink=False
+        self,
+        path_info,
+        checksum,
+        force,
+        progress_callback=None,
+        relink=False,
+        filter_info=None,
    ):
        # Create dir separately so that dir is created
        # even if there are no files in it
@@ -858,7 +886,7 @@ class RemoteBASE(object):

        dir_info = self.get_dir_cache(checksum)

-        logger.debug("Linking directory '{}'.".format(path_info))
+        logger.debug("Linking directory '{}'.", path_info)

        for entry in dir_info:
            relative_path = entry[self.PARAM_RELPATH]
@@ -866,6 +894,9 @@ class RemoteBASE(object):
            entry_cache_info = self.checksum_to_path_info(entry_checksum)
            entry_info = path_info / relative_path

+            if filter_info and not entry_info.isin_or_eq(filter_info):
+                continue
+
            entry_checksum_info = {self.PARAM_CHECKSUM: entry_checksum}
            if relink or self.changed(entry_info, entry_checksum_info):
                self.safe_remove(entry_info, force=force)
@@ -896,6 +927,7 @@ class RemoteBASE(object):
        force=False,
        progress_callback=None,
        relink=False,
+        filter_info=None,
    ):
        if path_info.scheme not in ["local", self.scheme]:
            raise NotImplementedError
@@ -905,35 +937,42 @@ class RemoteBASE(object):
        skip = False
        if not checksum:
            logger.warning(
-                "No checksum info found for '{}'. "
-                "It won't be created.".format(str(path_info))
+                "No file hash info found for '{}'. " "It won't be created.",
+                path_info,
            )
            self.safe_remove(path_info, force=force)
            failed = path_info

        elif not relink and not self.changed(path_info, checksum_info):
-            msg = "Data '{}' didn't change."
-            logger.debug(msg.format(str(path_info)))
+            logger.debug("Data '{}' didn't change.", path_info)
            skip = True

-        elif self.changed_cache(checksum):
-            msg = "Cache '{}' not found. File '{}' won't be created."
-            logger.warning(msg.format(checksum, str(path_info)))
+        elif self.changed_cache(
+            checksum, path_info=path_info, filter_info=filter_info
+        ):
+            logger.warning(
+                "Cache '{}' not found. File '{}' won't be created.",
+                checksum,
+                path_info,
+            )
            self.safe_remove(path_info, force=force)
            failed = path_info

        if failed or skip:
            if progress_callback:
                progress_callback(
-                    str(path_info), self.get_files_number(checksum)
+                    str(path_info),
+                    self.get_files_number(
+                        self.path_info, checksum, filter_info
+                    ),
                )
            return failed

-        msg = "Checking out '{}' with cache '{}'."
-        logger.debug(msg.format(str(path_info), checksum))
+        logger.debug("Checking out '{}' with cache '{}'.", path_info, checksum)

-        self._checkout(path_info, checksum, force, progress_callback, relink)
-        return None
+        self._checkout(
+            path_info, checksum, force, progress_callback, relink, filter_info
+        )

    def _checkout(
        self,
@@ -942,23 +981,32 @@ class RemoteBASE(object):
        force=False,
        progress_callback=None,
        relink=False,
+        filter_info=None,
    ):
        if not self.is_dir_checksum(checksum):
            return self._checkout_file(
                path_info, checksum, force, progress_callback=progress_callback
            )
        return self._checkout_dir(
-            path_info, checksum, force, progress_callback, relink
+            path_info, checksum, force, progress_callback, relink, filter_info
        )

-    def get_files_number(self, checksum):
+    def get_files_number(self, path_info, checksum, filter_info):
+        from funcy.py3 import ilen
+
        if not checksum:
            return 0

-        if self.is_dir_checksum(checksum):
+        if not self.is_dir_checksum(checksum):
+            return 1
+
+        if not filter_info:
            return len(self.get_dir_cache(checksum))

-        return 1
+        return ilen(
+            filter_info.isin_or_eq(path_info / entry[self.PARAM_CHECKSUM])
+            for entry in self.get_dir_cache(checksum)
+        )

    @staticmethod
    def unprotect(path_info):
@@ -977,3 +1025,6 @@ class RemoteBASE(object):

    def _update_unpacked_dir(self, checksum):
        pass
+
+    def _remove_unpacked_dir(self, checksum):
+        pass
@@ -1,157 +0,0 @@
-import logging
-import os
-import posixpath
-
-from dvc.config import Config
-from dvc.config import ConfigError
-from dvc.utils import relpath
-from dvc.utils.compat import urlparse
-
-
-logger = logging.getLogger(__name__)
-
-
-class RemoteConfig(object):
-    def __init__(self, config):
-        self.config = config
-
-    def get_settings(self, name):
-        """
-        Args:
-            name (str): The name of the remote that we want to retrieve
-
-        Returns:
-            dict: The content beneath the given remote name.
-
-        Example:
-            >>> config = {'remote "server"': {'url': 'ssh://localhost/'}}
-            >>> get_settings("server")
-            {'url': 'ssh://localhost/'}
-        """
-        settings = self.config.config.get(
-            Config.SECTION_REMOTE_FMT.format(name.lower())
-        )
-
-        if settings is None:
-            raise ConfigError(
-                "unable to find remote section '{}'".format(name)
-            )
-
-        parsed = urlparse(settings["url"])
-
-        # Support for cross referenced remotes.
-        # This will merge the settings, giving priority to the outer reference.
-        # For example, having:
-        #
-        #       dvc remote add server ssh://localhost
-        #       dvc remote modify server user root
-        #       dvc remote modify server ask_password true
-        #
-        #       dvc remote add images remote://server/tmp/pictures
-        #       dvc remote modify images user alice
-        #       dvc remote modify images ask_password false
-        #       dvc remote modify images password asdf1234
-        #
-        # Results on a config dictionary like:
-        #
-        #       {
-        #           "url": "ssh://localhost/tmp/pictures",
-        #           "user": "alice",
-        #           "password": "asdf1234",
-        #           "ask_password": False,
-        #       }
-        #
-        if parsed.scheme == "remote":
-            reference = self.get_settings(parsed.netloc)
-            url = posixpath.join(reference["url"], parsed.path.lstrip("/"))
-            merged = reference.copy()
-            merged.update(settings)
-            merged["url"] = url
-            return merged
-
-        return settings
-
-    @staticmethod
-    def resolve_path(path, config_file):
-        """Resolve path relative to config file location.
-
-        Args:
-            path: Path to be resolved.
-            config_file: Path to config file, which `path` is specified
-                relative to.
-
-        Returns:
-            Path relative to the `config_file` location. If `path` is an
-            absolute path then it will be returned without change.
-
-        """
-        if os.path.isabs(path):
-            return path
-        return relpath(path, os.path.dirname(config_file))
-
-    def add(self, name, url, default=False, force=False, level=None):
-        from dvc.remote import _get, RemoteLOCAL
-
-        configobj = self.config.get_configobj(level)
-        remote = _get({Config.SECTION_REMOTE_URL: url})
-        if remote == RemoteLOCAL and not url.startswith("remote://"):
-            url = self.resolve_path(url, configobj.filename)
-
-        self.config.set(
-            Config.SECTION_REMOTE_FMT.format(name),
-            Config.SECTION_REMOTE_URL,
-            url,
-            force=force,
-            level=level,
-        )
-        if default:
-            self.config.set(
-                Config.SECTION_CORE,
-                Config.SECTION_CORE_REMOTE,
-                name,
-                level=level,
-            )
-
-    def remove(self, name, level=None):
-        self.config.unset(Config.SECTION_REMOTE_FMT.format(name), level=level)
-
-        if level is None:
-            level = Config.LEVEL_REPO
-
-        for lev in [
-            Config.LEVEL_LOCAL,
-            Config.LEVEL_REPO,
-            Config.LEVEL_GLOBAL,
-            Config.LEVEL_SYSTEM,
-        ]:
-            self.config.unset(
-                Config.SECTION_CORE,
-                Config.SECTION_CORE_REMOTE,
-                level=lev,
-                force=True,
-            )
-            if lev == level:
-                break
-
-    def modify(self, name, option, value, level=None):
-        self.config.set(
-            Config.SECTION_REMOTE_FMT.format(name), option, value, level=level
-        )
-
-    def list(self, level=None):
-        return self.config.list_options(
-            Config.SECTION_REMOTE_REGEX, Config.SECTION_REMOTE_URL, level=level
-        )
-
-    def set_default(self, name, unset=False, level=None):
-        if unset:
-            self.config.unset(Config.SECTION_CORE, Config.SECTION_CORE_REMOTE)
-            return
-        self.config.set(
-            Config.SECTION_CORE, Config.SECTION_CORE_REMOTE, name, level=level
-        )
-
-    def get_default(self, level=None):
-        return self.config.get(
-            Config.SECTION_CORE, Config.SECTION_CORE_REMOTE, level=level
-        )
@@ -1,9 +1,9 @@
-from __future__ import unicode_literals
-
 import os
 import posixpath
 import logging
+import re
 import threading
+from urllib.parse import urlparse

 from funcy import retry, compose, decorator, wrap_with
 from funcy.py3 import cat
@@ -12,88 +12,246 @@ from dvc.progress import Tqdm
 from dvc.scheme import Schemes
 from dvc.path_info import CloudURLInfo
 from dvc.remote.base import RemoteBASE
-from dvc.config import Config
 from dvc.exceptions import DvcException
-from dvc.utils import tmp_fname
+from dvc.utils import tmp_fname, format_link

 logger = logging.getLogger(__name__)
 FOLDER_MIME_TYPE = "application/vnd.google-apps.folder"


 class GDriveRetriableError(DvcException):
-    def __init__(self, msg):
-        super(GDriveRetriableError, self).__init__(msg)
+    pass
+
+
+class GDrivePathNotFound(DvcException):
+    def __init__(self, path_info):
+        super().__init__("Google Drive path '{}' not found.".format(path_info))
+
+
+class GDriveAccessTokenRefreshError(DvcException):
+    def __init__(self):
+        super().__init__("Google Drive access token refreshment is failed.")
+
+
+class GDriveMissedCredentialKeyError(DvcException):
+    def __init__(self, path):
+        super().__init__(
+            "Google Drive user credentials file '{}' "
+            "misses value for key.".format(path)
+        )


@decorator
 def _wrap_pydrive_retriable(call):
-    from apiclient import errors
-    from pydrive.files import ApiRequestError
+    from pydrive2.files import ApiRequestError

    try:
        result = call()
-    except (ApiRequestError, errors.HttpError) as exception:
+    except ApiRequestError as exception:
        retry_codes = ["403", "500", "502", "503", "504"]
        if any(
            "HttpError {}".format(code) in str(exception)
            for code in retry_codes
        ):
-            raise GDriveRetriableError(msg="Google API request failed")
+            raise GDriveRetriableError("Google API request failed")
        raise
    return result


 gdrive_retry = compose(
-    # 8 tries, start at 0.5s, multiply by golden ratio, cap at 10s
+    # 15 tries, start at 0.5s, multiply by golden ratio, cap at 20s
    retry(
-        8, GDriveRetriableError, timeout=lambda a: min(0.5 * 1.618 ** a, 10)
+        15, GDriveRetriableError, timeout=lambda a: min(0.5 * 1.618 ** a, 20)
    ),
    _wrap_pydrive_retriable,
 )


+class GDriveURLInfo(CloudURLInfo):
+    def __init__(self, url):
+        super().__init__(url)
+
+        # GDrive URL host part is case sensitive,
+        # we are restoring it here.
+        p = urlparse(url)
+        self.host = p.netloc
+        assert self.netloc == self.host
+
+        # Normalize path. Important since we have a cache (path to ID)
+        # and don't want to deal with different variations of path in it.
+        self._spath = re.sub("/{2,}", "/", self._spath.rstrip("/"))
+
+
 class RemoteGDrive(RemoteBASE):
    scheme = Schemes.GDRIVE
-    path_cls = CloudURLInfo
-    REQUIRES = {"pydrive": "pydrive"}
+    path_cls = GDriveURLInfo
+    REQUIRES = {"pydrive2": "pydrive2"}
+    DEFAULT_NO_TRAVERSE = False
+    DEFAULT_VERIFY = True
+
    GDRIVE_USER_CREDENTIALS_DATA = "GDRIVE_USER_CREDENTIALS_DATA"
    DEFAULT_USER_CREDENTIALS_FILE = "gdrive-user-credentials.json"

    def __init__(self, repo, config):
-        super(RemoteGDrive, self).__init__(repo, config)
-        self.no_traverse = False
-        self.path_info = self.path_cls(config[Config.SECTION_REMOTE_URL])
-        self.config = config
-        self.init_drive()
+        super().__init__(repo, config)
+        self.path_info = self.path_cls(config["url"])

-    def init_drive(self):
-        self.client_id = self.config.get(Config.SECTION_GDRIVE_CLIENT_ID, None)
-        self.client_secret = self.config.get(
-            Config.SECTION_GDRIVE_CLIENT_SECRET, None
-        )
-        if not self.client_id or not self.client_secret:
+        if not self.path_info.bucket:
+            raise DvcException(
+                "Empty Google Drive URL '{}'. Learn more at "
+                "{}.".format(
+                    config["url"],
+                    format_link("https://man.dvc.org/remote/add"),
+                )
+            )
+
+        self._bucket = self.path_info.bucket
+        self._client_id = config.get("gdrive_client_id")
+        self._client_secret = config.get("gdrive_client_secret")
+        if not self._client_id or not self._client_secret:
            raise DvcException(
                "Please specify Google Drive's client id and "
-                "secret in DVC's config. Learn more at "
-                "https://man.dvc.org/remote/add."
+                "secret in DVC config. Learn more at "
+                "{}.".format(format_link("https://man.dvc.org/remote/add"))
            )
-        self.gdrive_user_credentials_path = (
-            tmp_fname(".dvc/tmp/")
+        self._gdrive_user_credentials_path = (
+            tmp_fname(os.path.join(self.repo.tmp_dir, ""))
            if os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA)
-            else self.config.get(
-                Config.SECTION_GDRIVE_USER_CREDENTIALS_FILE,
+            else config.get(
+                "gdrive_user_credentials_file",
                os.path.join(
                    self.repo.tmp_dir, self.DEFAULT_USER_CREDENTIALS_FILE
                ),
            )
        )

+        self._list_params = None
+        self._gdrive = None
+
+        self._cache_initialized = False
+        self._remote_root_id = None
+        self._cached_dirs = None
+        self._cached_ids = None
+
+    @property
+    @wrap_with(threading.RLock())
+    def drive(self):
+        from pydrive2.auth import RefreshError
+
+        if not self._gdrive:
+            from pydrive2.auth import GoogleAuth
+            from pydrive2.drive import GoogleDrive
+
+            if os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA):
+                with open(
+                    self._gdrive_user_credentials_path, "w"
+                ) as credentials_file:
+                    credentials_file.write(
+                        os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA)
+                    )
+
+            GoogleAuth.DEFAULT_SETTINGS["client_config_backend"] = "settings"
+            GoogleAuth.DEFAULT_SETTINGS["client_config"] = {
+                "client_id": self._client_id,
+                "client_secret": self._client_secret,
+                "auth_uri": "https://accounts.google.com/o/oauth2/auth",
+                "token_uri": "https://oauth2.googleapis.com/token",
+                "revoke_uri": "https://oauth2.googleapis.com/revoke",
+                "redirect_uri": "",
+            }
+            GoogleAuth.DEFAULT_SETTINGS["save_credentials"] = True
+            GoogleAuth.DEFAULT_SETTINGS["save_credentials_backend"] = "file"
+            GoogleAuth.DEFAULT_SETTINGS[
+                "save_credentials_file"
+            ] = self._gdrive_user_credentials_path
+            GoogleAuth.DEFAULT_SETTINGS["get_refresh_token"] = True
+            GoogleAuth.DEFAULT_SETTINGS["oauth_scope"] = [
+                "https://www.googleapis.com/auth/drive",
+                "https://www.googleapis.com/auth/drive.appdata",
+            ]
+
+            # Pass non existent settings path to force DEFAULT_SETTINGS loading
+            gauth = GoogleAuth(settings_file="")
+
+            try:
+                gauth.CommandLineAuth()
+            except RefreshError as exc:
+                raise GDriveAccessTokenRefreshError from exc
+            except KeyError as exc:
+                raise GDriveMissedCredentialKeyError(
+                    self._gdrive_user_credentials_path
+                ) from exc
+            # Handle pydrive2.auth.AuthenticationError and other auth failures
+            except Exception as exc:
+                raise DvcException(
+                    "Google Drive authentication failed"
+                ) from exc
+            finally:
+                if os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA):
+                    os.remove(self._gdrive_user_credentials_path)
+
+            self._gdrive = GoogleDrive(gauth)
+
+        return self._gdrive
+
+    @wrap_with(threading.RLock())
+    def _initialize_cache(self):
+        if self._cache_initialized:
+            return
+
+        cached_dirs = {}
+        cached_ids = {}
+        self._remote_root_id = self._get_remote_id(self.path_info)
+        for dir1 in self.gdrive_list_item(
+            "'{}' in parents and trashed=false".format(self._remote_root_id)
+        ):
+            remote_path = posixpath.join(self.path_info.path, dir1["title"])
+            cached_dirs.setdefault(remote_path, []).append(dir1["id"])
+            cached_ids[dir1["id"]] = dir1["title"]
+
+        self._cached_dirs = cached_dirs
+        self._cached_ids = cached_ids
+        self._cache_initialized = True
+
+    @property
+    def cached_dirs(self):
+        if not self._cache_initialized:
+            self._initialize_cache()
+        return self._cached_dirs
+
+    @property
+    def cached_ids(self):
+        if not self._cache_initialized:
+            self._initialize_cache()
+        return self._cached_ids
+
+    @property
+    def remote_root_id(self):
+        if not self._cache_initialized:
+            self._initialize_cache()
+        return self._remote_root_id
+
+    @property
+    def list_params(self):
+        if not self._list_params:
+            params = {"corpora": "default"}
+            if self._bucket != "root" and self._bucket != "appDataFolder":
+                params["driveId"] = self._get_remote_drive_id(self._bucket)
+                params["corpora"] = "drive"
+            self._list_params = params
+        return self._list_params
+
    @gdrive_retry
    def gdrive_upload_file(
-        self, args, no_progress_bar=True, from_file="", progress_name=""
+        self,
+        parent_id,
+        title,
+        no_progress_bar=True,
+        from_file="",
+        progress_name="",
    ):
        item = self.drive.CreateFile(
-            {"title": args["title"], "parents": [{"id": args["parent_id"]}]}
+            {"title": title, "parents": [{"id": parent_id}]}
        )

        with open(from_file, "rb") as fobj:
@@ -116,9 +274,11 @@ class RemoteGDrive(RemoteBASE):
    def gdrive_download_file(
        self, file_id, to_file, progress_name, no_progress_bar
    ):
-        gdrive_file = self.drive.CreateFile({"id": file_id})
+        param = {"id": file_id}
+        # it does not create a file on the remote
+        gdrive_file = self.drive.CreateFile(param)
        bar_format = (
-            "Donwloading {desc:{ncols_desc}.{ncols_desc}}... "
+            "Downloading {desc:{ncols_desc}.{ncols_desc}}... "
            + Tqdm.format_sizeof(int(gdrive_file["fileSize"]), "B", 1024)
        )
        with Tqdm(
@@ -127,7 +287,10 @@ class RemoteGDrive(RemoteBASE):
            gdrive_file.GetContentFile(to_file)

    def gdrive_list_item(self, query):
-        file_list = self.drive.ListFile({"q": query, "maxResults": 1000})
+        param = {"q": query, "maxResults": 1000}
+        param.update(self.list_params)
+
+        file_list = self.drive.ListFile(param)

        # Isolate and decorate fetching of remote drive items in pages
        get_list = gdrive_retry(lambda: next(file_list, None))
@@ -135,166 +298,132 @@ class RemoteGDrive(RemoteBASE):
        # Fetch pages until None is received, lazily flatten the thing
        return cat(iter(get_list, None))

-    def cache_root_dirs(self):
-        cached_dirs = {}
-        cached_ids = {}
-        for dir1 in self.gdrive_list_item(
-            "'{}' in parents and trashed=false".format(self.root_id)
-        ):
-            remote_path = posixpath.join(self.path_info.path, dir1["title"])
-            cached_dirs.setdefault(remote_path, []).append(dir1["id"])
-            cached_ids[dir1["id"]] = dir1["title"]
-        return cached_dirs, cached_ids
-
-    @property
-    def cached_dirs(self):
-        if not hasattr(self, "_cached_dirs"):
-            self.drive
-        return self._cached_dirs
-
-    @property
-    def cached_ids(self):
-        if not hasattr(self, "_cached_ids"):
-            self.drive
-        return self._cached_ids
-
-    @property
    @wrap_with(threading.RLock())
-    def drive(self):
-        if not hasattr(self, "_gdrive"):
-            from pydrive.auth import GoogleAuth
-            from pydrive.drive import GoogleDrive
+    def gdrive_create_dir(self, parent_id, title, remote_path):
+        if parent_id == self.remote_root_id:
+            cached = self.cached_dirs.get(remote_path, [])
+            if cached:
+                return cached[0]

-            if os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA):
-                with open(
-                    self.gdrive_user_credentials_path, "w"
-                ) as credentials_file:
-                    credentials_file.write(
-                        os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA)
-                    )
+        item = self._create_remote_dir(parent_id, title)

-            GoogleAuth.DEFAULT_SETTINGS["client_config_backend"] = "settings"
-            GoogleAuth.DEFAULT_SETTINGS["client_config"] = {
-                "client_id": self.client_id,
-                "client_secret": self.client_secret,
-                "auth_uri": "https://accounts.google.com/o/oauth2/auth",
-                "token_uri": "https://oauth2.googleapis.com/token",
-                "revoke_uri": "https://oauth2.googleapis.com/revoke",
-                "redirect_uri": "",
-            }
-            GoogleAuth.DEFAULT_SETTINGS["save_credentials"] = True
-            GoogleAuth.DEFAULT_SETTINGS["save_credentials_backend"] = "file"
-            GoogleAuth.DEFAULT_SETTINGS[
-                "save_credentials_file"
-            ] = self.gdrive_user_credentials_path
-            GoogleAuth.DEFAULT_SETTINGS["get_refresh_token"] = True
-            GoogleAuth.DEFAULT_SETTINGS["oauth_scope"] = [
-                "https://www.googleapis.com/auth/drive",
-                "https://www.googleapis.com/auth/drive.appdata",
-            ]
+        if parent_id == self.remote_root_id:
+            self.cached_dirs.setdefault(remote_path, []).append(item["id"])
+            self.cached_ids[item["id"]] = item["title"]

-            # Pass non existent settings path to force DEFAULT_SETTINGS loading
-            gauth = GoogleAuth(settings_file="")
-            gauth.CommandLineAuth()
-
-            if os.getenv(RemoteGDrive.GDRIVE_USER_CREDENTIALS_DATA):
-                os.remove(self.gdrive_user_credentials_path)
-
-            self._gdrive = GoogleDrive(gauth)
-
-            self.root_id = self.get_remote_id(self.path_info, create=True)
-            self._cached_dirs, self._cached_ids = self.cache_root_dirs()
-
-        return self._gdrive
+        return item["id"]

    @gdrive_retry
-    def create_remote_dir(self, parent_id, title):
+    def _create_remote_dir(self, parent_id, title):
+        parent = {"id": parent_id}
        item = self.drive.CreateFile(
-            {
-                "title": title,
-                "parents": [{"id": parent_id}],
-                "mimeType": FOLDER_MIME_TYPE,
-            }
+            {"title": title, "parents": [parent], "mimeType": FOLDER_MIME_TYPE}
        )
        item.Upload()
        return item

    @gdrive_retry
-    def get_remote_item(self, name, parents_ids):
+    def _delete_remote_file(self, remote_id):
+        param = {"id": remote_id}
+        # it does not create a file on the remote
+        item = self.drive.CreateFile(param)
+        item.Delete()
+
+    @gdrive_retry
+    def _get_remote_item(self, name, parents_ids):
        if not parents_ids:
            return None
-        query = " or ".join(
-            "'{}' in parents".format(parent_id) for parent_id in parents_ids
+        query = "({})".format(
+            " or ".join(
+                "'{}' in parents".format(parent_id)
+                for parent_id in parents_ids
+            )
        )

        query += " and trashed=false and title='{}'".format(name)

+        # Remote might contain items with duplicated path (titles).
+        # We thus limit number of items.
+        param = {"q": query, "maxResults": 1}
+        param.update(self.list_params)
+
        # Limit found remote items count to 1 in response
-        item_list = self.drive.ListFile(
-            {"q": query, "maxResults": 1}
-        ).GetList()
+        item_list = self.drive.ListFile(param).GetList()
        return next(iter(item_list), None)

-    def resolve_remote_item_from_path(self, path_parts, create):
-        parents_ids = ["root"]
-        current_path = ""
-        for path_part in path_parts:
-            current_path = posixpath.join(current_path, path_part)
-            remote_ids = self.get_remote_id_from_cache(current_path)
-            if remote_ids:
-                parents_ids = remote_ids
-                continue
-            item = self.get_remote_item(path_part, parents_ids)
-            if not item and create:
-                item = self.create_remote_dir(parents_ids[0], path_part)
-            elif not item:
-                return None
-            parents_ids = [item["id"]]
-        return item
+    @gdrive_retry
+    def _get_remote_drive_id(self, remote_id):
+        param = {"id": remote_id}
+        # it does not create a file on the remote
+        item = self.drive.CreateFile(param)
+        item.FetchMetadata("driveId")
+        return item.get("driveId", None)

-    def get_remote_id_from_cache(self, remote_path):
-        if hasattr(self, "_cached_dirs"):
-            return self.cached_dirs.get(remote_path, [])
+    def _get_cached_remote_ids(self, path):
+        if not path:
+            return [self._bucket]
+        if self._cache_initialized:
+            if path == self.path_info.path:
+                return [self.remote_root_id]
+            return self.cached_dirs.get(path, [])
        return []

-    def get_remote_id(self, path_info, create=False):
-        remote_ids = self.get_remote_id_from_cache(path_info.path)
-
+    def _path_to_remote_ids(self, path, create):
+        remote_ids = self._get_cached_remote_ids(path)
        if remote_ids:
-            return remote_ids[0]
+            return remote_ids

-        file1 = self.resolve_remote_item_from_path(
-            path_info.path.split("/"), create
-        )
-        return file1["id"] if file1 else ""
+        parent_path, part = posixpath.split(path)
+        parent_ids = self._path_to_remote_ids(parent_path, create)
+        item = self._get_remote_item(part, parent_ids)
+
+        if not item:
+            return (
+                [self.gdrive_create_dir(parent_ids[0], part, path)]
+                if create
+                else []
+            )
+
+        return [item["id"]]
+
+    def _get_remote_id(self, path_info, create=False):
+        assert path_info.bucket == self._bucket
+
+        remote_ids = self._path_to_remote_ids(path_info.path, create)
+        if not remote_ids:
+            raise GDrivePathNotFound(path_info)
+
+        return remote_ids[0]

    def exists(self, path_info):
-        return self.get_remote_id(path_info) != ""
+        try:
+            self._get_remote_id(path_info)
+        except GDrivePathNotFound:
+            return False
+        else:
+            return True

    def _upload(self, from_file, to_info, name, no_progress_bar):
        dirname = to_info.parent
-        if dirname:
-            parent_id = self.get_remote_id(dirname, True)
-        else:
-            parent_id = to_info.bucket
+        assert dirname
+        parent_id = self._get_remote_id(dirname, True)

        self.gdrive_upload_file(
-            {"title": to_info.name, "parent_id": parent_id},
-            no_progress_bar,
-            from_file,
-            name,
+            parent_id, to_info.name, no_progress_bar, from_file, name
        )

    def _download(self, from_info, to_file, name, no_progress_bar):
-        file_id = self.get_remote_id(from_info)
+        file_id = self._get_remote_id(from_info)
        self.gdrive_download_file(file_id, to_file, name, no_progress_bar)

    def all(self):
        if not self.cached_ids:
            return

-        query = " or ".join(
-            "'{}' in parents".format(dir_id) for dir_id in self.cached_ids
+        query = "({})".format(
+            " or ".join(
+                "'{}' in parents".format(dir_id) for dir_id in self.cached_ids
+            )
        )

        query += " and trashed=false"
@@ -306,3 +435,7 @@ class RemoteGDrive(RemoteBASE):
            except ValueError:
                # We ignore all the non-cache looking files
                logger.debug('Ignoring path as "non-cache looking"')
+
+    def remove(self, path_info):
+        remote_id = self._get_remote_id(path_info)
+        self._delete_remote_file(remote_id)
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals, division
-
 import logging
 from datetime import timedelta
 from functools import wraps
@@ -9,13 +7,11 @@ import threading

 from funcy import cached_property, wrap_prop

-from dvc.config import Config
 from dvc.exceptions import DvcException
 from dvc.path_info import CloudURLInfo
 from dvc.progress import Tqdm
 from dvc.remote.base import RemoteBASE
 from dvc.scheme import Schemes
-from dvc.utils.compat import FileNotFoundError  # skipcq: PYL-W0622

 logger = logging.getLogger(__name__)

@@ -76,13 +72,13 @@ class RemoteGS(RemoteBASE):
    PARAM_CHECKSUM = "md5"

    def __init__(self, repo, config):
-        super(RemoteGS, self).__init__(repo, config)
+        super().__init__(repo, config)

-        url = config.get(Config.SECTION_REMOTE_URL, "gs:///")
+        url = config.get("url", "gs:///")
        self.path_info = self.path_cls(url)

-        self.projectname = config.get(Config.SECTION_GCP_PROJECTNAME, None)
-        self.credentialpath = config.get(Config.SECTION_GCP_CREDENTIALPATH)
+        self.projectname = config.get("projectname", None)
+        self.credentialpath = config.get("credentialpath")

    @wrap_prop(threading.Lock())
    @cached_property
@@ -1,18 +1,15 @@
-from __future__ import unicode_literals
-
-from dvc.utils.compat import FileNotFoundError, urlparse
 import io
 import logging
 import os
 import posixpath
 import re
+import subprocess
 from collections import deque
 from contextlib import closing, contextmanager
-import subprocess
+from urllib.parse import urlparse

 from .base import RemoteBASE, RemoteCmdError
 from .pool import get_connection
-from dvc.config import Config
 from dvc.scheme import Schemes
 from dvc.utils import fix_env, tmp_fname

@@ -26,15 +23,14 @@ class RemoteHDFS(RemoteBASE):
    REQUIRES = {"pyarrow": "pyarrow"}

    def __init__(self, repo, config):
-        super(RemoteHDFS, self).__init__(repo, config)
+        super().__init__(repo, config)
        self.path_info = None
-        url = config.get(Config.SECTION_REMOTE_URL)
+        url = config.get("url")
        if not url:
            return

        parsed = urlparse(url)
-
-        user = parsed.username or config.get(Config.SECTION_REMOTE_USER)
+        user = parsed.username or config.get("user")

        self.path_info = self.path_cls.from_parts(
            scheme=self.scheme,
@@ -1,17 +1,13 @@
-from __future__ import unicode_literals
-
 import logging
 import threading

 from funcy import cached_property, wrap_prop

-from dvc.config import Config
 from dvc.config import ConfigError
 from dvc.exceptions import DvcException, HTTPError
 from dvc.progress import Tqdm
 from dvc.remote.base import RemoteBASE
 from dvc.scheme import Schemes
-from dvc.utils.compat import open

 logger = logging.getLogger(__name__)

@@ -25,9 +21,9 @@ class RemoteHTTP(RemoteBASE):
    PARAM_CHECKSUM = "etag"

    def __init__(self, repo, config):
-        super(RemoteHTTP, self).__init__(repo, config)
+        super().__init__(repo, config)

-        url = config.get(Config.SECTION_REMOTE_URL)
+        url = config.get("url")
        self.path_info = self.path_cls(url) if url else None

        if not self.no_traverse:
@@ -104,7 +100,22 @@ class RemoteHTTP(RemoteBASE):
        kwargs.setdefault("timeout", self.REQUEST_TIMEOUT)

        try:
-            return self._session.request(method, url, **kwargs)
+            res = self._session.request(method, url, **kwargs)
+
+            redirect_no_location = (
+                kwargs["allow_redirects"]
+                and res.status_code in (301, 302)
+                and "location" not in res.headers
+            )
+
+            if redirect_no_location:
+                # AWS s3 doesn't like to add a location header to its redirects
+                # from https://s3.amazonaws.com/<bucket name>/* type URLs.
+                # This should be treated as an error
+                raise requests.exceptions.RequestException
+
+            return res
+
        except requests.exceptions.RequestException:
            raise DvcException("could not perform a {} request".format(method))

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 from .http import RemoteHTTP
 from dvc.scheme import Schemes

@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import errno
 import logging
 import os
@@ -9,30 +7,17 @@ from functools import partial

 from shortuuid import uuid

-from dvc.config import Config
-from dvc.exceptions import DownloadError
-from dvc.exceptions import DvcException
-from dvc.exceptions import UploadError
+from dvc.compat import fspath_py35
+from dvc.exceptions import DvcException, DownloadError, UploadError
 from dvc.path_info import PathInfo
 from dvc.progress import Tqdm
-from dvc.remote.base import RemoteBASE
-from dvc.remote.base import STATUS_DELETED
-from dvc.remote.base import STATUS_MAP
-from dvc.remote.base import STATUS_MISSING
-from dvc.remote.base import STATUS_NEW
+from dvc.remote.base import RemoteBASE, STATUS_MAP
+from dvc.remote.base import STATUS_DELETED, STATUS_MISSING, STATUS_NEW
 from dvc.scheme import Schemes
+from dvc.scm.tree import is_working_tree
 from dvc.system import System
-from dvc.utils import copyfile
-from dvc.utils import file_md5
-from dvc.utils import makedirs
-from dvc.utils import relpath
-from dvc.utils import tmp_fname
-from dvc.utils import walk_files
-from dvc.utils.compat import fspath_py35
-from dvc.utils.compat import open
-from dvc.utils.compat import str
-from dvc.utils.fs import move
-from dvc.utils.fs import remove
+from dvc.utils import file_md5, relpath, tmp_fname
+from dvc.utils.fs import copyfile, move, makedirs, remove, walk_files

 logger = logging.getLogger(__name__)

@@ -50,23 +35,17 @@ class RemoteLOCAL(RemoteBASE):
    SHARED_MODE_MAP = {None: (0o644, 0o755), "group": (0o664, 0o775)}

    def __init__(self, repo, config):
-        super(RemoteLOCAL, self).__init__(repo, config)
-        self.protected = config.get(Config.SECTION_CACHE_PROTECTED, False)
+        super().__init__(repo, config)
+        self.protected = config.get("protected", False)

-        shared = config.get(Config.SECTION_CACHE_SHARED)
+        shared = config.get("shared")
        self._file_mode, self._dir_mode = self.SHARED_MODE_MAP[shared]

        if self.protected:
            # cache files are set to be read-only for everyone
            self._file_mode = stat.S_IREAD | stat.S_IRGRP | stat.S_IROTH

-        cache_dir = config.get(Config.SECTION_REMOTE_URL)
-
-        if cache_dir is not None and not os.path.isabs(cache_dir):
-            cwd = config[Config.PRIVATE_CWD]
-            cache_dir = os.path.abspath(os.path.join(cwd, cache_dir))
-
-        self.path_info = PathInfo(cache_dir) if cache_dir else None
+        self.cache_dir = config.get("url")
        self._dir_info = {}

    @property
@@ -77,13 +56,17 @@ class RemoteLOCAL(RemoteBASE):
    def cache_dir(self):
        return self.path_info.fspath if self.path_info else None

+    @cache_dir.setter
+    def cache_dir(self, value):
+        self.path_info = PathInfo(value) if value else None
+
    @classmethod
    def supported(cls, config):
        return True

    def list_cache_paths(self):
        assert self.path_info is not None
-        return walk_files(self.path_info, None)
+        return walk_files(self.path_info)

    def get(self, md5):
        if not md5:
@@ -138,7 +121,9 @@ class RemoteLOCAL(RemoteBASE):
        return os.path.getsize(fspath_py35(path_info))

    def walk_files(self, path_info):
-        for fname in walk_files(path_info, self.repo.dvcignore):
+        assert is_working_tree(self.repo.tree)
+
+        for fname in self.repo.tree.walk_files(path_info):
            yield PathInfo(fname)

    def get_file_checksum(self, path_info):
@@ -177,6 +162,10 @@ class RemoteLOCAL(RemoteBASE):
    def symlink(from_info, to_info):
        System.symlink(from_info, to_info)

+    @staticmethod
+    def is_symlink(path_info):
+        return System.is_symlink(path_info)
+
    def hardlink(self, from_info, to_info):
        # If there are a lot of empty files (which happens a lot in datasets),
        # and the cache type is `hardlink`, we might reach link limits and
@@ -203,6 +192,10 @@ class RemoteLOCAL(RemoteBASE):

        System.hardlink(from_info, to_info)

+    @staticmethod
+    def is_hardlink(path_info):
+        return System.is_hardlink(path_info)
+
    @staticmethod
    def reflink(from_info, to_info):
        System.reflink(from_info, to_info)
@@ -407,7 +400,7 @@ class RemoteLOCAL(RemoteBASE):
    def _unprotect_file(path):
        if System.is_symlink(path) or System.is_hardlink(path):
            logger.debug("Unprotecting '{}'".format(path))
-            tmp = os.path.join(os.path.dirname(path), "." + str(uuid()))
+            tmp = os.path.join(os.path.dirname(path), "." + uuid())

            # The operations order is important here - if some application
            # would access the file during the process of copyfile then it
@@ -427,7 +420,9 @@ class RemoteLOCAL(RemoteBASE):
        os.chmod(path, os.stat(path).st_mode | stat.S_IWRITE)

    def _unprotect_dir(self, path):
-        for fname in walk_files(path, self.repo.dvcignore):
+        assert is_working_tree(self.repo.tree)
+
+        for fname in self.repo.tree.walk_files(path):
            RemoteLOCAL._unprotect_file(fname)

    def unprotect(self, path_info):
@@ -463,6 +458,10 @@ class RemoteLOCAL(RemoteBASE):
        info = self.checksum_to_path_info(checksum)
        return info.with_name(info.name + self.UNPACKED_DIR_SUFFIX)

+    def _remove_unpacked_dir(self, checksum):
+        path_info = self._get_unpacked_dir_path_info(checksum)
+        self.remove(path_info)
+
    def _path_info_changed(self, path_info):
        if self.exists(path_info) and self.state.get(path_info):
            return False
@@ -1,13 +1,9 @@
-from __future__ import absolute_import
-from __future__ import unicode_literals
-
 import logging
 import os
 import threading

 from funcy import cached_property, wrap_prop

-from dvc.config import Config
 from dvc.path_info import CloudURLInfo
 from dvc.progress import Tqdm
 from dvc.remote.base import RemoteBASE
@@ -43,23 +39,21 @@ class RemoteOSS(RemoteBASE):
    COPY_POLL_SECONDS = 5

    def __init__(self, repo, config):
-        super(RemoteOSS, self).__init__(repo, config)
+        super().__init__(repo, config)

-        url = config.get(Config.SECTION_REMOTE_URL)
+        url = config.get("url")
        self.path_info = self.path_cls(url) if url else None

-        self.endpoint = config.get(Config.SECTION_OSS_ENDPOINT) or os.getenv(
-            "OSS_ENDPOINT"
-        )
+        self.endpoint = config.get("oss_endpoint") or os.getenv("OSS_ENDPOINT")

        self.key_id = (
-            config.get(Config.SECTION_OSS_ACCESS_KEY_ID)
+            config.get("oss_key_id")
            or os.getenv("OSS_ACCESS_KEY_ID")
            or "defaultId"
        )

        self.key_secret = (
-            config.get(Config.SECTION_OSS_ACCESS_KEY_SECRET)
+            config.get("oss_key_secret")
            or os.getenv("OSS_ACCESS_KEY_SECRET")
            or "defaultSecret"
        )
@@ -1,5 +1,4 @@
 # -*- coding: utf-8 -*-
-from __future__ import unicode_literals

 import logging
 import os
@@ -7,7 +6,7 @@ import threading

 from funcy import cached_property, wrap_prop

-from dvc.config import Config, ConfigError
+from dvc.config import ConfigError
 from dvc.exceptions import DvcException
 from dvc.exceptions import ETagMismatchError
 from dvc.path_info import CloudURLInfo
@@ -25,37 +24,35 @@ class RemoteS3(RemoteBASE):
    PARAM_CHECKSUM = "etag"

    def __init__(self, repo, config):
-        super(RemoteS3, self).__init__(repo, config)
+        super().__init__(repo, config)

-        url = config.get(Config.SECTION_REMOTE_URL, "s3://")
+        url = config.get("url", "s3://")
        self.path_info = self.path_cls(url)

-        self.region = config.get(Config.SECTION_AWS_REGION)
+        self.region = config.get("region")
+        self.profile = config.get("profile")
+        self.endpoint_url = config.get("endpointurl")

-        self.profile = config.get(Config.SECTION_AWS_PROFILE)
-
-        self.endpoint_url = config.get(Config.SECTION_AWS_ENDPOINT_URL)
-
-        if config.get(Config.SECTION_AWS_LIST_OBJECTS):
+        if config.get("listobjects"):
            self.list_objects_api = "list_objects"
        else:
            self.list_objects_api = "list_objects_v2"

-        self.use_ssl = config.get(Config.SECTION_AWS_USE_SSL, True)
+        self.use_ssl = config.get("use_ssl", True)

        self.extra_args = {}

-        self.sse = config.get(Config.SECTION_AWS_SSE, "")
+        self.sse = config.get("sse")
        if self.sse:
            self.extra_args["ServerSideEncryption"] = self.sse

-        self.acl = config.get(Config.SECTION_AWS_ACL, "")
+        self.acl = config.get("acl")
        if self.acl:
            self.extra_args["ACL"] = self.acl

        self._append_aws_grants_to_extra_args(config)

-        shared_creds = config.get(Config.SECTION_AWS_CREDENTIALPATH)
+        shared_creds = config.get("credentialpath")
        if shared_creds:
            os.environ.setdefault("AWS_SHARED_CREDENTIALS_FILE", shared_creds)

@@ -88,8 +85,8 @@ class RemoteS3(RemoteBASE):
            obj = s3.head_object(Bucket=bucket, Key=path, *args, **kwargs)
        except Exception as exc:
            raise DvcException(
-                "s3://{}/{} does not exist".format(bucket, path), exc
-            )
+                "s3://{}/{} does not exist".format(bucket, path)
+            ) from exc
        return obj

    @classmethod
@@ -157,6 +154,7 @@ class RemoteS3(RemoteBASE):
        # the same throughout the transfer, so it means that in order to
        # preserve etag, we need to transfer each part separately, so the
        # object is transfered in the same chunks as it was originally.
+        from boto3.s3.transfer import TransferConfig

        obj = cls.get_head_object(s3, from_info.bucket, from_info.path)
        etag = obj["ETag"].strip('"')
@@ -170,7 +168,13 @@ class RemoteS3(RemoteBASE):
            )
        else:
            source = {"Bucket": from_info.bucket, "Key": from_info.path}
-            s3.copy(source, to_info.bucket, to_info.path, ExtraArgs=extra_args)
+            s3.copy(
+                source,
+                to_info.bucket,
+                to_info.path,
+                ExtraArgs=extra_args,
+                Config=TransferConfig(multipart_threshold=size + 1),
+            )

        cached_etag = cls.get_etag(s3, to_info.bucket, to_info.path)
        if etag != cached_etag:
@@ -195,11 +199,7 @@ class RemoteS3(RemoteBASE):
        }
        paginator = self.s3.get_paginator(self.list_objects_api)
        for page in paginator.paginate(**kwargs):
-            contents = page.get("Contents", None)
-            if not contents:
-                continue
-            for item in contents:
-                yield item
+            yield from page.get("Contents", ())

    def _list_paths(self, path_info, max_items=None):
        return (
@@ -320,14 +320,14 @@ class RemoteS3(RemoteBASE):
        """

        grants = {
-            Config.SECTION_AWS_GRANT_FULL_CONTROL: "GrantFullControl",
-            Config.SECTION_AWS_GRANT_READ: "GrantRead",
-            Config.SECTION_AWS_GRANT_READ_ACP: "GrantReadACP",
-            Config.SECTION_AWS_GRANT_WRITE_ACP: "GrantWriteACP",
+            "grant_full_control": "GrantFullControl",
+            "grant_read": "GrantRead",
+            "grant_read_acp": "GrantReadACP",
+            "grant_write_acp": "GrantWriteACP",
        }

        for grant_option, extra_args_key in grants.items():
-            if config.get(grant_option, ""):
+            if config.get(grant_option):
                if self.acl:
                    raise ConfigError(
                        "`acl` and `grant_*` AWS S3 config options "
@@ -1,12 +1,10 @@
 import logging
 import sys
 import time
+
 from functools import wraps
-
 import colorama

-from dvc.config import Config
-

 logger = logging.getLogger(__name__)
 this = sys.modules[__name__]
@@ -31,11 +29,9 @@ def slow_link_guard(f):
        if this.already_displayed:
            return f(remote, *args, **kwargs)

-        config = remote.repo.config.config.get(Config.SECTION_CACHE, {})
-        cache_type = config.get(Config.SECTION_CACHE_TYPE)
-        should_warn = config.get(Config.SECTION_CACHE_SLOW_LINK_WARNING, True)
-
-        if not should_warn or cache_type:
+        cache_conf = remote.repo.config["cache"]
+        slow_link_warning = cache_conf.get("slow_link_warning", True)
+        if not slow_link_warning or cache_conf.get("type"):
            return f(remote, *args, **kwargs)

        start = time.time()
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import errno
 import getpass
 import io
@@ -9,18 +7,16 @@ import os
 import threading
 from concurrent.futures import ThreadPoolExecutor
 from contextlib import closing, contextmanager
+from urllib.parse import urlparse

-from funcy import memoize, wrap_with
+from funcy import memoize, wrap_with, silent, first

 import dvc.prompt as prompt
-from dvc.config import Config
 from dvc.progress import Tqdm
 from dvc.remote.base import RemoteBASE
 from dvc.remote.pool import get_connection
 from dvc.scheme import Schemes
 from dvc.utils import to_chunks
-from dvc.utils.compat import StringIO
-from dvc.utils.compat import urlparse

 logger = logging.getLogger(__name__)

@@ -52,21 +48,21 @@ class RemoteSSH(RemoteBASE):
    DEFAULT_CACHE_TYPES = ["copy"]

    def __init__(self, repo, config):
-        super(RemoteSSH, self).__init__(repo, config)
-        url = config.get(Config.SECTION_REMOTE_URL)
+        super().__init__(repo, config)
+        url = config.get("url")
        if url:
            parsed = urlparse(url)
            user_ssh_config = self._load_user_ssh_config(parsed.hostname)

            host = user_ssh_config.get("hostname", parsed.hostname)
            user = (
-                config.get(Config.SECTION_REMOTE_USER)
+                config.get("user")
                or parsed.username
                or user_ssh_config.get("user")
                or getpass.getuser()
            )
            port = (
-                config.get(Config.SECTION_REMOTE_PORT)
+                config.get("port")
                or parsed.port
                or self._try_get_ssh_config_port(user_ssh_config)
                or self.DEFAULT_PORT
@@ -83,14 +79,12 @@ class RemoteSSH(RemoteBASE):
            user_ssh_config = {}

        self.keyfile = config.get(
-            Config.SECTION_REMOTE_KEY_FILE
+            "keyfile"
        ) or self._try_get_ssh_config_keyfile(user_ssh_config)
-        self.timeout = config.get(Config.SECTION_REMOTE_TIMEOUT, self.TIMEOUT)
-        self.password = config.get(Config.SECTION_REMOTE_PASSWORD, None)
-        self.ask_password = config.get(
-            Config.SECTION_REMOTE_ASK_PASSWORD, False
-        )
-        self.gss_auth = config.get(Config.SECTION_REMOTE_GSS_AUTH, False)
+        self.timeout = config.get("timeout", self.TIMEOUT)
+        self.password = config.get("password", None)
+        self.ask_password = config.get("ask_password", False)
+        self.gss_auth = config.get("gss_auth", False)

    @staticmethod
    def ssh_config_filename():
@@ -106,24 +100,18 @@ class RemoteSSH(RemoteBASE):
            ssh_config = paramiko.SSHConfig()
            with open(user_config_file) as f:
                # For whatever reason parsing directly from f is unreliable
-                f_copy = StringIO(f.read())
+                f_copy = io.StringIO(f.read())
                ssh_config.parse(f_copy)
            user_ssh_config = ssh_config.lookup(hostname)
        return user_ssh_config

    @staticmethod
    def _try_get_ssh_config_port(user_ssh_config):
-        try:
-            return int(user_ssh_config.get("port"))
-        except (ValueError, TypeError):
-            return None
+        return silent(int)(user_ssh_config.get("port"))

    @staticmethod
    def _try_get_ssh_config_keyfile(user_ssh_config):
-        identity_file = user_ssh_config.get("identityfile")
-        if identity_file and len(identity_file) > 0:
-            return identity_file[0]
-        return None
+        return first(user_ssh_config.get("identityfile") or ())

    def ensure_credentials(self, path_info=None):
        if path_info is None:
@@ -263,8 +251,7 @@ class RemoteSSH(RemoteBASE):
    def list_cache_paths(self):
        with self.ssh(self.path_info) as ssh:
            # If we simply return an iterator then with above closes instantly
-            for path in ssh.walk_files(self.path_info.path):
-                yield path
+            yield from ssh.walk_files(self.path_info.path)

    def walk_files(self, path_info):
        with self.ssh(path_info) as ssh:
@@ -3,6 +3,7 @@ import logging
 import os
 import posixpath
 import stat
+from contextlib import suppress

 from funcy import cached_property

@@ -12,7 +13,6 @@ except ImportError:
    paramiko = None

 from dvc.utils import tmp_fname
-from dvc.utils.compat import ignore_file_not_found
 from dvc.progress import Tqdm
 from dvc.exceptions import DvcException
 from dvc.remote.base import RemoteCmdError
@@ -60,13 +60,13 @@ class SSHConnection:
        self._ssh.close()

    def st_mode(self, path):
-        with ignore_file_not_found():
+        with suppress(FileNotFoundError):
            return self.sftp.lstat(path).st_mode

        return 0

    def getsize(self, path):
-        with ignore_file_not_found():
+        with suppress(FileNotFoundError):
            return self.sftp.lstat(path).st_size

        return 0
@@ -103,14 +103,13 @@ class SSHConnection:
        if tail:
            try:
                self.sftp.mkdir(path)
-            except IOError as e:
+            except IOError as exc:
                # Since paramiko errors are very vague we need to recheck
                # whether it's because path already exists or something else
-                if e.errno == errno.EACCES or not self.exists(path):
+                if exc.errno == errno.EACCES or not self.exists(path):
                    raise DvcException(
-                        "unable to create remote directory '{}'".format(path),
-                        cause=e,
-                    )
+                        "unable to create remote directory '{}'".format(path)
+                    ) from exc

    def walk(self, directory, topdown=True):
        # NOTE: original os.walk() implementation [1] with default options was
@@ -123,9 +122,8 @@ class SSHConnection:
            raise DvcException(
                "couldn't get the '{}' remote directory files list".format(
                    directory
-                ),
-                cause=exc,
-            )
+                )
+            ) from exc

        dirs = []
        nondirs = []
@@ -141,8 +139,7 @@ class SSHConnection:

        for dname in dirs:
            newpath = posixpath.join(directory, dname)
-            for entry in self.walk(newpath, topdown=topdown):
-                yield entry
+            yield from self.walk(newpath, topdown=topdown)

        if not topdown:
            yield directory, dirs, nondirs
@@ -153,22 +150,20 @@ class SSHConnection:
                yield posixpath.join(root, fname)

    def _remove_file(self, path):
-        with ignore_file_not_found():
+        with suppress(FileNotFoundError):
            self.sftp.remove(path)

    def _remove_dir(self, path):
        for root, dirs, files in self.walk(path, topdown=False):
            for fname in files:
-                path = posixpath.join(root, fname)
-                with ignore_file_not_found():
-                    self._remove_file(path)
+                with suppress(FileNotFoundError):
+                    self._remove_file(posixpath.join(root, fname))

            for dname in dirs:
-                path = posixpath.join(root, dname)
-                with ignore_file_not_found():
-                    self.sftp.rmdir(dname)
+                with suppress(FileNotFoundError):
+                    self.sftp.rmdir(posixpath.join(root, dname))

-        with ignore_file_not_found():
+        with suppress(FileNotFoundError):
            self.sftp.rmdir(path)

    def remove(self, path):
@@ -1,32 +1,23 @@
-from __future__ import unicode_literals
-
-import logging
 import os
 from contextlib import contextmanager
 from functools import wraps
 from itertools import chain

-from funcy import cached_property
+from dvc.ignore import CleanTree
+from dvc.compat import fspath_py35
+
+from funcy import cached_property, cat

-from .graph import check_acyclic
-from .graph import get_pipeline
-from .graph import get_pipelines
-from .graph import get_stages
 from dvc.config import Config
-from dvc.exceptions import FileMissingError
-from dvc.exceptions import NotDvcRepoError
-from dvc.exceptions import OutputNotFoundError
-from dvc.ignore import DvcIgnoreFilter
+from dvc.exceptions import (
+    FileMissingError,
+    NotDvcRepoError,
+    OutputNotFoundError,
+)
 from dvc.path_info import PathInfo
 from dvc.remote.base import RemoteActionNotImplemented
-from dvc.utils import relpath
 from dvc.utils.fs import path_isin
-from dvc.utils.compat import FileNotFoundError
-from dvc.utils.compat import fspath_py35
-from dvc.utils.compat import open as _open
-
-
-logger = logging.getLogger(__name__)
+from .graph import check_acyclic, get_pipeline, get_pipelines


 def locked(f):
@@ -48,6 +39,7 @@ class Repo(object):
    from dvc.repo.install import install
    from dvc.repo.add import add
    from dvc.repo.remove import remove
+    from dvc.repo.ls import ls
    from dvc.repo.lock import lock as lock_stage
    from dvc.repo.move import move
    from dvc.repo.run import run
@@ -76,7 +68,7 @@ class Repo(object):
        from dvc.repo.metrics import Metrics
        from dvc.scm.tree import WorkingTree
        from dvc.repo.tag import Tag
-        from dvc.utils import makedirs
+        from dvc.utils.fs import makedirs

        root_dir = self.find_root(root_dir)

@@ -92,7 +84,7 @@ class Repo(object):
        self.tmp_dir = os.path.join(self.dvc_dir, "tmp")
        makedirs(self.tmp_dir, exist_ok=True)

-        hardlink_lock = self.config.config["core"].get("hardlink_lock", False)
+        hardlink_lock = self.config["core"].get("hardlink_lock", False)
        self.lock = make_lock(
            os.path.join(self.dvc_dir, "lock"),
            tmp_dir=os.path.join(self.dvc_dir, "tmp"),
@@ -102,13 +94,7 @@ class Repo(object):

        # NOTE: storing state and link_state in the repository itself to avoid
        # any possible state corruption in 'shared cache dir' scenario.
-        self.state = State(self, self.config.config)
-
-        core = self.config.config[Config.SECTION_CORE]
-
-        level = core.get(Config.SECTION_CORE_LOGLEVEL)
-        if level:
-            logger.setLevel(level.upper())
+        self.state = State(self)

        self.cache = Cache(self)
        self.cloud = DataCloud(self)
@@ -124,29 +110,34 @@ class Repo(object):

    @tree.setter
    def tree(self, tree):
-        self._tree = tree
+        self._tree = tree if isinstance(tree, CleanTree) else CleanTree(tree)
        # Our graph cache is no longer valid, as it was based on the previous
        # tree.
        self._reset()

    def __repr__(self):
-        return "Repo: '{root_dir}'".format(root_dir=self.root_dir)
+        return "{}: '{}'".format(self.__class__.__name__, self.root_dir)

    @classmethod
    def find_root(cls, root=None):
-        if root is None:
-            root = os.getcwd()
-        else:
-            root = os.path.abspath(os.path.realpath(root))
+        root_dir = os.path.realpath(root or os.curdir)
+
+        if not os.path.isdir(root_dir):
+            raise NotDvcRepoError("directory '{}' does not exist".format(root))

        while True:
-            dvc_dir = os.path.join(root, cls.DVC_DIR)
+            dvc_dir = os.path.join(root_dir, cls.DVC_DIR)
            if os.path.isdir(dvc_dir):
-                return root
-            if os.path.ismount(root):
+                return root_dir
+            if os.path.ismount(root_dir):
                break
-            root = os.path.dirname(root)
-        raise NotDvcRepoError(root)
+            root_dir = os.path.dirname(root_dir)
+
+        message = (
+            "you are not inside of a DVC repository "
+            "(checked up to mount point '{}')"
+        ).format(root_dir)
+        raise NotDvcRepoError(message)

    @classmethod
    def find_dvc_dir(cls, root=None):
@@ -169,7 +160,7 @@ class Repo(object):
        updater = Updater(self.dvc_dir)

        flist = (
-            [self.config.config_local_file, updater.updater_file]
+            [self.config.files["local"], updater.updater_file]
            + [self.lock.lockfile, updater.lock.lockfile, self.tmp_dir]
            + self.state.files
        )
@@ -190,32 +181,32 @@ class Repo(object):
        G = graph or self.graph

        if not target:
-            return get_stages(G)
+            return list(G)

        target = os.path.abspath(target)

        if recursive and os.path.isdir(target):
-            attrs = nx.get_node_attributes(G, "stage")
-            nodes = [node for node in nx.dfs_postorder_nodes(G)]
-
-            ret = []
-            for node in nodes:
-                stage = attrs[node]
-                if path_isin(stage.path, target):
-                    ret.append(stage)
-            return ret
+            stages = nx.dfs_postorder_nodes(G)
+            return [stage for stage in stages if path_isin(stage.path, target)]

        stage = Stage.load(self, target)
        if not with_deps:
            return [stage]

-        node = relpath(stage.path, self.root_dir)
-        pipeline = get_pipeline(get_pipelines(G), node)
+        pipeline = get_pipeline(get_pipelines(G), stage)
+        return list(nx.dfs_postorder_nodes(pipeline, stage))

-        return [
-            pipeline.node[n]["stage"]
-            for n in nx.dfs_postorder_nodes(pipeline, node)
-        ]
+    def collect_granular(self, target, *args, **kwargs):
+        if not target:
+            return [(stage, None) for stage in self.stages]
+
+        try:
+            (out,) = self.find_outs_by_path(target, strict=False)
+            filter_info = PathInfo(os.path.abspath(target))
+            return [(out.stage, filter_info)]
+        except OutputNotFoundError:
+            stages = self.collect(target, *args, **kwargs)
+            return [(stage, None) for stage in stages]

    def used_cache(
        self,
@@ -251,28 +242,24 @@ class Repo(object):
            all_tags=all_tags,
            all_commits=all_commits,
        ):
-            if targets:
-                stages = []
-                for target in targets:
-                    collected = self.collect(
-                        target, recursive=recursive, with_deps=with_deps
-                    )
-                    stages.extend(collected)
-            else:
-                stages = self.stages
+            targets = targets or [None]

-            for stage in stages:
-                if stage.is_repo_import:
-                    dep, = stage.deps
-                    cache.external[dep.repo_pair].add(dep.def_path)
-                    continue
+            pairs = cat(
+                self.collect_granular(
+                    target, recursive=recursive, with_deps=with_deps
+                )
+                for target in targets
+            )

-                for out in stage.outs:
-                    used_cache = out.get_used_cache(
-                        remote=remote, force=force, jobs=jobs
-                    )
-                    suffix = "({})".format(branch) if branch else ""
-                    cache.update(used_cache, suffix=suffix)
+            suffix = "({})".format(branch) if branch else ""
+            for stage, filter_info in pairs:
+                used_cache = stage.get_used_cache(
+                    remote=remote,
+                    force=force,
+                    jobs=jobs,
+                    filter_info=filter_info,
+                )
+                cache.update(used_cache, suffix=suffix)

        return cache

@@ -323,44 +310,50 @@ class Repo(object):
        )

        G = nx.DiGraph()
-        stages = stages or self.collect_stages()
+        stages = stages or self.stages
        stages = [stage for stage in stages if stage]
        outs = {}

        for stage in stages:
            for out in stage.outs:
                if out.path_info in outs:
-                    stages = [stage.relpath, outs[out.path_info].stage.relpath]
-                    raise OutputDuplicationError(str(out), stages)
+                    dup_stages = [stage, outs[out.path_info].stage]
+                    raise OutputDuplicationError(str(out), dup_stages)
                outs[out.path_info] = out

        for stage in stages:
            for out in stage.outs:
                for p in out.path_info.parents:
                    if p in outs:
-                        raise OverlappingOutputPathsError(outs[p], out)
+                        msg = (
+                            "Paths for outs:\n'{}'('{}')\n'{}'('{}')\n"
+                            "overlap. To avoid unpredictable behaviour, "
+                            "rerun command with non overlapping outs paths."
+                        ).format(
+                            str(outs[p]),
+                            outs[p].stage.relpath,
+                            str(out),
+                            out.stage.relpath,
+                        )
+                        raise OverlappingOutputPathsError(outs[p], out, msg)

        for stage in stages:
            stage_path_info = PathInfo(stage.path)
            for p in chain([stage_path_info], stage_path_info.parents):
                if p in outs:
-                    raise StagePathAsOutputError(stage.wdir, stage.relpath)
+                    raise StagePathAsOutputError(stage, str(outs[p]))

        for stage in stages:
-            node = relpath(stage.path, self.root_dir)
-
-            G.add_node(node, stage=stage)
+            G.add_node(stage)

            for dep in stage.deps:
                if dep.path_info is None:
                    continue

-                for out in outs:
-                    if out.overlaps(dep.path_info):
-                        dep_stage = outs[out].stage
-                        dep_node = relpath(dep_stage.path, self.root_dir)
-                        G.add_node(dep_node, stage=dep_stage)
-                        G.add_edge(node, dep_node)
+                for out_path_info, out in outs.items():
+                    if out_path_info.overlaps(dep.path_info):
+                        G.add_node(out.stage)
+                        G.add_edge(stage, out.stage)

        check_acyclic(G)

@@ -374,18 +367,8 @@ class Repo(object):
    def pipelines(self):
        return get_pipelines(self.graph)

-    @staticmethod
-    def _filter_out_dirs(dirs, outs, root_dir):
-        def filter_dirs(dname):
-            path = os.path.join(root_dir, dname)
-            for out in outs:
-                if path == os.path.normpath(out):
-                    return False
-            return True
-
-        return list(filter(filter_dirs, dirs))
-
-    def collect_stages(self):
+    @cached_property
+    def stages(self):
        """
        Walks down the root directory looking for Dvcfiles,
        skipping the directories that are related with
@@ -398,41 +381,37 @@ class Repo(object):
        from dvc.stage import Stage

        stages = []
-        outs = []
+        outs = set()

-        for root, dirs, files in self.tree.walk(
-            self.root_dir, dvcignore=self.dvcignore
-        ):
+        for root, dirs, files in self.tree.walk(self.root_dir):
            for fname in files:
                path = os.path.join(root, fname)
                if not Stage.is_valid_filename(path):
                    continue
                stage = Stage.load(self, path)
-                for out in stage.outs:
-                    if out.scheme == "local":
-                        outs.append(out.fspath + out.sep)
                stages.append(stage)

-            dirs[:] = self._filter_out_dirs(dirs, outs, root)
+                for out in stage.outs:
+                    if out.scheme == "local":
+                        outs.add(out.fspath)
+
+            dirs[:] = [d for d in dirs if os.path.join(root, d) not in outs]

        return stages

-    @cached_property
-    def stages(self):
-        return get_stages(self.graph)
-
-    def find_outs_by_path(self, path, outs=None, recursive=False):
+    def find_outs_by_path(self, path, outs=None, recursive=False, strict=True):
        if not outs:
            outs = [out for stage in self.stages for out in stage.outs]

        abs_path = os.path.abspath(path)
-        is_dir = self.tree.isdir(abs_path)
+        path_info = PathInfo(abs_path)
+        match = path_info.__eq__ if strict else path_info.isin_or_eq

        def func(out):
-            if out.scheme == "local" and out.fspath == abs_path:
+            if out.scheme == "local" and match(out.path_info):
                return True

-            if is_dir and recursive and out.path_info.isin(abs_path):
+            if recursive and out.path_info.isin(path_info):
                return True

            return False
@@ -445,7 +424,7 @@ class Repo(object):

    def find_out_by_relpath(self, relpath):
        path = os.path.join(self.root_dir, relpath)
-        out, = self.find_outs_by_path(path)
+        (out,) = self.find_outs_by_path(path)
        return out

    def is_dvc_internal(self, path):
@@ -453,29 +432,30 @@ class Repo(object):
        return self.DVC_DIR in path_parts

    @contextmanager
-    def open(self, path, remote=None, mode="r", encoding=None):
+    def open_by_relpath(self, path, remote=None, mode="r", encoding=None):
        """Opens a specified resource as a file descriptor"""
        cause = None
        try:
-            out, = self.find_outs_by_path(path)
-        except OutputNotFoundError as e:
+            out = self.find_out_by_relpath(path)
+        except OutputNotFoundError as exc:
            out = None
-            cause = e
+            cause = exc

        if out and out.use_cache:
            try:
                with self._open_cached(out, remote, mode, encoding) as fd:
                    yield fd
                return
-            except FileNotFoundError as e:
-                raise FileMissingError(relpath(path, self.root_dir), cause=e)
+            except FileNotFoundError as exc:
+                raise FileMissingError(path) from exc

-        if self.tree.exists(path):
-            with self.tree.open(path, mode, encoding) as fd:
+        abs_path = os.path.join(self.root_dir, path)
+        if os.path.exists(abs_path):
+            with open(abs_path, mode=mode, encoding=encoding) as fd:
                yield fd
            return

-        raise FileMissingError(relpath(path, self.root_dir), cause=cause)
+        raise FileMissingError(path) from cause

    def _open_cached(self, out, remote=None, mode="r", encoding=None):
        if out.isdir():
@@ -485,7 +465,7 @@ class Repo(object):
        cache_file = fspath_py35(cache_file)

        if os.path.exists(cache_file):
-            return _open(cache_file, mode=mode, encoding=encoding)
+            return open(cache_file, mode=mode, encoding=encoding)

        try:
            remote_obj = self.cloud.get_remote(remote)
@@ -496,11 +476,7 @@ class Repo(object):
                cache_info = out.get_used_cache(remote=remote)
                self.cloud.pull(cache_info, remote=remote)

-            return _open(cache_file, mode=mode, encoding=encoding)
-
-    @cached_property
-    def dvcignore(self):
-        return DvcIgnoreFilter(self.root_dir, self.tree)
+            return open(cache_file, mode=mode, encoding=encoding)

    def close(self):
        self.scm.close()
@@ -1,18 +1,18 @@
-from __future__ import unicode_literals
-
 import logging
 import os

 import colorama
-from six import string_types

 from . import locked
-from dvc.exceptions import RecursiveAddingWhileUsingFilename
-from dvc.progress import Tqdm
-from dvc.repo.scm_context import scm_context
-from dvc.stage import Stage
-from dvc.utils import LARGE_DIR_SIZE
-from dvc.utils import walk_files
+from ..exceptions import (
+    RecursiveAddingWhileUsingFilename,
+    OverlappingOutputPathsError,
+)
+from ..output.base import OutputDoesNotExistError
+from ..progress import Tqdm
+from ..repo.scm_context import scm_context
+from ..stage import Stage
+from ..utils import LARGE_DIR_SIZE

 logger = logging.getLogger(__name__)

@@ -23,11 +23,16 @@ def add(repo, targets, recursive=False, no_commit=False, fname=None):
    if recursive and fname:
        raise RecursiveAddingWhileUsingFilename()

-    if isinstance(targets, string_types):
+    if isinstance(targets, str):
        targets = [targets]

    stages_list = []
-    with Tqdm(total=len(targets), desc="Add", unit="file", leave=True) as pbar:
+    num_targets = len(targets)
+    with Tqdm(total=num_targets, desc="Add", unit="file", leave=True) as pbar:
+        if num_targets == 1:
+            # clear unneeded top-level progress bar for single target
+            pbar.bar_format = "Adding..."
+            pbar.refresh()
        for target in targets:
            sub_targets = _find_all_targets(repo, target, recursive)
            pbar.total += len(sub_targets) - 1
@@ -47,19 +52,46 @@ def add(repo, targets, recursive=False, no_commit=False, fname=None):

            stages = _create_stages(repo, sub_targets, fname, pbar=pbar)

-            repo.check_modified_graph(stages)
+            try:
+                repo.check_modified_graph(stages)
+            except OverlappingOutputPathsError as exc:
+                msg = (
+                    "Cannot add '{out}', because it is overlapping with other "
+                    "DVC tracked output: '{parent}'.\n"
+                    "To include '{out}' in '{parent}', run "
+                    "'dvc commit {parent_stage}'"
+                ).format(
+                    out=exc.overlapping_out.path_info,
+                    parent=exc.parent.path_info,
+                    parent_stage=exc.parent.stage.relpath,
+                )
+                raise OverlappingOutputPathsError(
+                    exc.parent, exc.overlapping_out, msg
+                )

-            for stage in stages:
-                stage.save()
+            with Tqdm(
+                total=len(stages),
+                desc="Processing",
+                unit="file",
+                disable=len(stages) == 1,
+            ) as pbar_stages:
+                for stage in stages:
+                    try:
+                        stage.save()
+                    except OutputDoesNotExistError:
+                        pbar.n -= 1
+                        raise

-                if not no_commit:
-                    stage.commit()
+                    if not no_commit:
+                        stage.commit()

-                stage.dump()
+                    stage.dump()
+                    pbar_stages.update()

            stages_list += stages
-        # remove filled bar bit of progress, leaving stats
-        pbar.bar_format = pbar.BAR_FMT_DEFAULT.replace("|{bar:10}|", " ")
+
+        if num_targets == 1:  # restore bar format for stats
+            pbar.bar_format = pbar.BAR_FMT_DEFAULT

    return stages_list

@@ -68,7 +100,12 @@ def _find_all_targets(repo, target, recursive):
    if os.path.isdir(target) and recursive:
        return [
            fname
-            for fname in walk_files(target, repo.dvcignore)
+            for fname in Tqdm(
+                repo.tree.walk_files(target),
+                desc="Searching " + target,
+                bar_format=Tqdm.BAR_FMT_NOTOTAL,
+                unit="file",
+            )
            if not repo.is_dvc_internal(fname)
            if not Stage.is_stage_file(fname)
            if not repo.scm.belongs_to_scm(fname)
@@ -80,8 +117,15 @@ def _find_all_targets(repo, target, recursive):
 def _create_stages(repo, targets, fname, pbar=None):
    stages = []

-    for out in targets:
-        stage = Stage.create(repo, outs=[out], add=True, fname=fname)
+    for out in Tqdm(
+        targets,
+        desc="Creating DVC-files",
+        disable=len(targets) < LARGE_DIR_SIZE,
+        unit="file",
+    ):
+        stage = Stage.create(
+            repo, outs=[out], accompany_outs=True, fname=fname
+        )

        if not stage:
            if pbar is not None:
@@ -4,12 +4,7 @@ from dvc.scm.tree import WorkingTree


 def brancher(  # noqa: E302
-    self,
-    branches=None,
-    all_branches=False,
-    tags=None,
-    all_tags=False,
-    all_commits=False,
+    self, revs=None, all_branches=False, all_tags=False, all_commits=False
 ):
    """Generator that iterates over specified revisions.

@@ -25,12 +20,12 @@ def brancher(  # noqa: E302
            - empty string it there is no branches to iterate over
            - "Working Tree" if there are uncommitted changes in the SCM repo
    """
-    if not any([branches, all_branches, tags, all_tags, all_commits]):
+    if not any([revs, all_branches, all_tags, all_commits]):
        yield ""
        return

    saved_tree = self.tree
-    revs = []
+    revs = revs or []

    scm = self.scm

@@ -41,24 +36,15 @@ def brancher(  # noqa: E302
        revs = scm.list_all_commits()
    else:
        if all_branches:
-            branches = scm.list_branches()
+            revs.extend(scm.list_branches())

        if all_tags:
-            tags = scm.list_tags()
+            revs.extend(scm.list_tags())

-        if branches is not None:
-            revs.extend(branches)
-
-        if tags is not None:
-            revs.extend(tags)
-
-    # NOTE: it might be a good idea to wrap this loop in try/finally block
-    # to don't leave the tree on some unexpected branch after the
-    # `brancher()`, but this could cause problems on exception handling
-    # code which might expect the tree on which exception was raised to
-    # stay in place. This behavior is a subject to change.
-    for sha, names in group_by(scm.resolve_rev, revs).items():
-        self.tree = scm.get_tree(sha)
-        yield ", ".join(names)
-
-    self.tree = saved_tree
+    try:
+        if revs:
+            for sha, names in group_by(scm.resolve_rev, revs).items():
+                self.tree = scm.get_tree(sha)
+                yield ", ".join(names)
+    finally:
+        self.tree = saved_tree
@@ -1,5 +1,3 @@
-from __future__ import unicode_literals
-
 import logging

 from dvc.exceptions import CheckoutError
@@ -20,8 +18,10 @@ def _cleanup_unused_links(repo):
    repo.state.remove_unused_links(used)


-def get_all_files_numbers(stages):
-    return sum(stage.get_all_files_number() for stage in stages)
+def get_all_files_numbers(pairs):
+    return sum(
+        stage.get_all_files_number(filter_info) for stage, filter_info in pairs
+    )


 def _checkout(
@@ -34,36 +34,37 @@ def _checkout(
 ):
    from dvc.stage import StageFileDoesNotExistError, StageFileBadNameError

-    stages = set()
-
    if not targets:
        targets = [None]
        _cleanup_unused_links(self)

+    pairs = set()
    for target in targets:
        try:
-            new = self.collect(
-                target, with_deps=with_deps, recursive=recursive
+            pairs.update(
+                self.collect_granular(
+                    target, with_deps=with_deps, recursive=recursive
+                )
            )
-            stages.update(new)
        except (StageFileDoesNotExistError, StageFileBadNameError) as exc:
            if not target:
                raise
-            raise CheckoutErrorSuggestGit(target, exc)
+            raise CheckoutErrorSuggestGit(target) from exc

-    total = get_all_files_numbers(stages)
+    total = get_all_files_numbers(pairs)
    if total == 0:
        logger.info("Nothing to do")
    failed = []
    with Tqdm(
        total=total, unit="file", desc="Checkout", disable=total == 0
    ) as pbar:
-        for stage in stages:
+        for stage, filter_info in pairs:
            failed.extend(
                stage.checkout(
                    force=force,
                    progress_callback=pbar.update_desc,
                    relink=relink,
+                    filter_info=filter_info,
                )
            )
    if failed:
@@ -1,8 +1,15 @@
 from dvc.utils.fs import remove
+from . import locked


-def destroy(self):
-    for stage in self.stages:
+@locked
+def _destroy_stages(repo):
+    for stage in repo.stages:
        stage.remove(remove_outs=False)

-    remove(self.dvc_dir)
+
+# NOTE: not locking `destroy`, as `remove` will need to delete `.dvc` dir,
+# which will cause issues on Windows, as `.dvc/lock` will be busy.
+def destroy(repo):
+    _destroy_stages(repo)
+    remove(repo.dvc_dir)
@@ -1,251 +1,76 @@
-from __future__ import unicode_literals
-
 import os
-from errno import ENOENT

-import dvc.logger as logger
-from . import locked
-from dvc.scm.base import FileNotInCommitError
-from dvc.scm.git import DIFF_A_REF
-from dvc.scm.git import DIFF_A_TREE
-from dvc.scm.git import DIFF_B_REF
-from dvc.scm.git import DIFF_B_TREE
-from dvc.scm.git import DIFF_EQUAL
-
-
-DIFF_TARGET = "target"
-DIFF_IS_DIR = "is_dir"
-DIFF_OLD_FILE = "old_file"
-DIFF_OLD_CHECKSUM = "old_checksum"
-DIFF_NEW_FILE = "new_file"
-DIFF_NEW_CHECKSUM = "new_checksum"
-DIFF_SIZE = "size_diff"
-DIFF_DEL = "del"
-DIFF_IDENT = "ident"
-DIFF_CHANGE = "changes"
-DIFF_NEW = "new"
-DIFF_MOVE = "moves"
-DIFF_LIST = "diffs"
-DIFF_SIZE_UNKNOWN = "?"
-DIFF_A_OUTPUT = "a_output"
-DIFF_B_OUTPUT = "b_output"
-DIFF_DELETED = "deleted_file"
-DIFF_IS_NEW = "created_file"
-
-
-def _file_not_exists(error, result):
-    if error.errno == ENOENT:
-        result.update({DIFF_SIZE: DIFF_SIZE_UNKNOWN})
-    else:
-        raise error
-
-
-def _extract_dir(self, dir_not_exists, output):
-    """Extract the content of dvc tree file
-    Args:
-        self(object) - Repo class instance
-        dir_not_exists(bool) - flag for directory existence
-        output(object) - OutputLOCAL class instance
-    Returns:
-        dict - dictionary with keys - paths to file in .dvc/cache
-                               values -checksums for that files
-    """
-    if not dir_not_exists:
-        lst = output.dir_cache
-        return {i["relpath"]: i["md5"] for i in lst}
-    return {}
-
-
-def _get_dir_info(dir_not_exists, a_output):
-    if not dir_not_exists:
-        return str(a_output), a_output.checksum
-    return "", ""
-
-
-def _ident_files(a_entries, b_entries):
-    keys = [
-        key for key in a_entries.keys() if b_entries.get(key) == a_entries[key]
-    ]
-    return len(keys)
-
-
-def _modified_files(self, a_entries, b_entries):
-    keys = [key for key in a_entries.keys() if key in b_entries]
-    diff_size = 0
-    modified_count = 0
-    for key in keys:
-        if a_entries[key] != b_entries[key]:
-            modified_count += 1
-            diff_size += os.path.getsize(
-                self.cache.local.get(b_entries[key])
-            ) - os.path.getsize(self.cache.local.get(a_entries[key]))
-    return modified_count, diff_size
-
-
-def _deleted_files(self, a_entries, b_entries):
-    diff_size = 0
-    deleted_count = 0
-    for key, value in a_entries.items():
-        if key not in b_entries:
-            deleted_count += 1
-            diff_size -= os.path.getsize(self.cache.local.get(a_entries[key]))
-    return deleted_count, diff_size
-
-
-def _new_files(self, a_entries, b_entries):
-    diff_size = 0
-    new_count = 0
-    for key, value in b_entries.items():
-        if key not in a_entries:
-            new_count += 1
-            diff_size += os.path.getsize(self.cache.local.get(b_entries[key]))
-    return new_count, diff_size
-
-
-def _get_tree_changes(self, a_entries, b_entries):
-    result = {
-        DIFF_DEL: 0,
-        DIFF_IDENT: 0,
-        DIFF_CHANGE: 0,
-        DIFF_NEW: 0,
-        DIFF_MOVE: 0,
-    }
-    result[DIFF_IDENT] = _ident_files(a_entries, b_entries)
-    result[DIFF_CHANGE], diff_size = _modified_files(
-        self, a_entries, b_entries
-    )
-    result[DIFF_SIZE] = diff_size
-    result[DIFF_DEL], diff_size = _deleted_files(self, a_entries, b_entries)
-    result[DIFF_SIZE] += diff_size
-    result[DIFF_NEW], diff_size = _new_files(self, a_entries, b_entries)
-    result[DIFF_SIZE] += diff_size
-    return result
-
-
-def _check_local_cache(a_out, is_checked):
-    if a_out is not None and a_out.scheme != "local":
-        is_checked.append(str(a_out))
-        return True
-    return False
-
-
-def _is_dir(path, a_outs, b_outs):
-    if a_outs.get(path):
-        return a_outs[path].is_dir_checksum
-    else:
-        return b_outs[path].is_dir_checksum
-
-
-def _get_diff_outs(self, diff_dct):
-    self.tree = diff_dct[DIFF_A_TREE]
-    a_outs = {str(out): out for st in self.stages for out in st.outs}
-    self.tree = diff_dct[DIFF_B_TREE]
-    b_outs = {str(out): out for st in self.stages for out in st.outs}
-    outs_paths = set(a_outs.keys())
-    outs_paths.update(b_outs.keys())
-    results = {}
-    non_local_cache = []
-    for path in outs_paths:
-        check1 = _check_local_cache(a_outs.get(path), non_local_cache)
-        check2 = _check_local_cache(b_outs.get(path), non_local_cache)
-        # skip files/directories with non-local cache for now
-        if check1 or check2:
-            continue
-        results[path] = {}
-        results[path][DIFF_A_OUTPUT] = a_outs.get(path)
-        results[path][DIFF_B_OUTPUT] = b_outs.get(path)
-        results[path][DIFF_IS_NEW] = path not in a_outs
-        results[path][DIFF_DELETED] = path not in b_outs
-        results[path][DIFF_IS_DIR] = _is_dir(path, a_outs, b_outs)
-    if non_local_cache:
-        logger.warning(
-            "Diff is not supported for non-local outputs. Ignoring: {}".format(
-                non_local_cache
-            )
-        )
-
-    return results
-
-
-def _diff_dir(self, target, diff_dct):
-    result = {DIFF_TARGET: target}
-    result[DIFF_IS_DIR] = True
-    a_entries, b_entries = {}, {}
-    try:
-        a_entries = _extract_dir(
-            self, diff_dct[DIFF_IS_NEW], diff_dct[DIFF_A_OUTPUT]
-        )
-        b_entries = _extract_dir(
-            self, diff_dct[DIFF_DELETED], diff_dct[DIFF_B_OUTPUT]
-        )
-        result[DIFF_OLD_FILE], result[DIFF_OLD_CHECKSUM] = _get_dir_info(
-            diff_dct[DIFF_IS_NEW], diff_dct[DIFF_A_OUTPUT]
-        )
-        result[DIFF_NEW_FILE], result[DIFF_NEW_CHECKSUM] = _get_dir_info(
-            diff_dct[DIFF_DELETED], diff_dct[DIFF_B_OUTPUT]
-        )
-        result.update(_get_tree_changes(self, a_entries, b_entries))
-    except IOError as e:
-        _file_not_exists(e, result)
-    return result
-
-
-def _diff_file(self, target, diff_dct):
-    result = {DIFF_TARGET: target}
-    size = 0
-    try:
-        if not diff_dct[DIFF_IS_NEW]:
-            result[DIFF_OLD_FILE] = target
-            result[DIFF_OLD_CHECKSUM] = diff_dct[DIFF_A_OUTPUT].checksum
-            size -= os.path.getsize(
-                self.cache.local.get(diff_dct[DIFF_A_OUTPUT].checksum)
-            )
-        if not diff_dct[DIFF_DELETED]:
-            result[DIFF_NEW_FILE] = target
-            result[DIFF_NEW_CHECKSUM] = diff_dct[DIFF_B_OUTPUT].checksum
-            size += os.path.getsize(
-                self.cache.local.get(diff_dct[DIFF_B_OUTPUT].checksum)
-            )
-        result[DIFF_SIZE] = size
-    except IOError as e:
-        _file_not_exists(e, result)
-    return result
-
-
-def _diff_royal(self, target, diff_dct):
-    if diff_dct[DIFF_IS_DIR]:
-        return _diff_dir(self, target, diff_dct)
-    return _diff_file(self, target, diff_dct)
+from dvc.exceptions import DvcException
+from dvc.repo import locked
+from dvc.scm.git import Git


@locked
-def diff(self, a_ref, target=None, b_ref=None):
-    """Generates diff message string output
-
-    Args:
-        target(str) - file/directory to check diff of
-        a_ref(str) - first tag
-        (optional) b_ref(str) - second git tag
-
-    Returns:
-        string: string of output message with diff info
+def diff(self, a_rev="HEAD", b_rev=None):
    """
-    result = {}
-    diff_dct = self.scm.get_diff_trees(a_ref, b_ref=b_ref)
-    result[DIFF_A_REF] = diff_dct[DIFF_A_REF]
-    result[DIFF_B_REF] = diff_dct[DIFF_B_REF]
-    if diff_dct[DIFF_EQUAL]:
-        result[DIFF_EQUAL] = True
+    By default, it compares the working tree with the last commit's tree.
+
+    This implementation differs from `git diff` since DVC doesn't have
+    the concept of `index`, but it keeps the same interface, thus,
+    `dvc diff` would be the same as `dvc diff HEAD`.
+    """
+    if type(self.scm) is not Git:
+        raise DvcException("only supported for Git repositories")
+
+    def _paths_checksums():
+        """
+        A dictionary of checksums addressed by relpaths collected from
+        the current tree outputs.
+
+        Unpack directories to include their entries
+
+        To help distinguish between a directory and a file output,
+        the former one will come with a trailing slash in the path:
+
+            directory: "data/"
+            file:      "data"
+        """
+        result = {}
+
+        for stage in self.stages:
+            for output in stage.outs:
+                if not output.is_dir_checksum:
+                    result.update({str(output): output.checksum})
+                    continue
+
+                result.update({os.path.join(str(output), ""): output.checksum})
+
+                for entry in output.dir_cache:
+                    path = str(output.path_info / entry["relpath"])
+                    result.update({path: entry["md5"]})
+
        return result
-    result[DIFF_LIST] = []
-    diff_outs = _get_diff_outs(self, diff_dct)
-    if target is None:
-        result[DIFF_LIST] = [
-            _diff_royal(self, path, diff_outs[path]) for path in diff_outs
-        ]
-    elif target in diff_outs:
-        result[DIFF_LIST] = [_diff_royal(self, target, diff_outs[target])]
-    else:
-        msg = "Have not found file/directory '{}' in the commits"
-        raise FileNotInCommitError(msg.format(target))
-    return result
+
+    working_tree = self.tree
+    a_tree = self.scm.get_tree(a_rev)
+    b_tree = self.scm.get_tree(b_rev) if b_rev else working_tree
+
+    try:
+        self.tree = a_tree
+        old = _paths_checksums()
+
+        self.tree = b_tree
+        new = _paths_checksums()
+    finally:
+        self.tree = working_tree
+
+    # Compare paths between the old and new tree.
+    # set() efficiently converts dict keys to a set
+    added = sorted(set(new) - set(old))
+    deleted = sorted(set(old) - set(new))
+    modified = sorted(set(old) & set(new))
+
+    return {
+        "added": [{"path": path, "checksum": new[path]} for path in added],
+        "deleted": [{"path": path, "checksum": old[path]} for path in deleted],
+        "modified": [
+            {"path": path, "checksum": {"old": old[path], "new": new[path]}}
+            for path in modified
+            if old[path] != new[path]
+        ],
+    }
@@ -1,12 +1,9 @@
-from __future__ import unicode_literals
-
 import logging

 from dvc.cache import NamedCache
 from dvc.config import NoRemoteError
 from dvc.exceptions import DownloadError
 from dvc.exceptions import OutputNotFoundError
-from dvc.external_repo import external_repo
 from dvc.scm.base import CloneError


@@ -72,11 +69,13 @@ def _fetch(


 def _fetch_external(self, repo_url, repo_rev, files):
-    failed = 0
+    from dvc.external_repo import external_repo

-    cache_dir = self.cache.local.cache_dir
+    failed = 0
    try:
-        with external_repo(repo_url, repo_rev, cache_dir=cache_dir) as repo:
+        with external_repo(repo_url, repo_rev) as repo:
+            repo.cache.local.cache_dir = self.cache.local.cache_dir
+
            with repo.state:
                cache = NamedCache()
                for name in files:
--- a/Show More
+++ b/Show More