Add dependency checking as config validation

dvc/remote/__init__.py

@@ -21,6 +21,6 @@ def supported_url(url):
 
 def Remote(project, config):
     for r in REMOTES:
-        if r.supported(config):
+        if r.supported(config, check_dependencies=True):
             return r(project, config)
     raise DvcException('Remote \'{}\' is not supported.'.format(config))

dvc/remote/base.py

@@ -33,14 +33,16 @@ class DataCloudError(DvcException):
 
 class RemoteBase(object):
     REGEX = None
+    REQUIRES = []
 
     def __init__(self, project, config):
         pass
 
     @classmethod
-    def supported(cls, config):
+    def supported(cls, config, check_dependencies=False):
         url = config[Config.SECTION_REMOTE_URL]
-        return cls.match(url) != None
+        deps_ok = not check_dependencies or all(cls.REQUIRES)
+        return cls.match(url) != None and deps_ok
 
     @classmethod
     def match(cls, url):

dvc/remote/gs.py

@@ -1,6 +1,10 @@
 import os
 import posixpath
-from google.cloud import storage
+
+try:
+    from google.cloud import storage
+except ImportError:
+    storage = None
 
 try:
     from urlparse import urlparse
@@ -16,6 +20,7 @@ from dvc.progress import progress
 class RemoteGS(RemoteBase):
     scheme = 'gs'
     REGEX = r'^gs://(?P<path>.*)$'
+    REQUIRES = RemoteBase.REQUIRES + [storage]
     PARAM_ETAG = 'etag'
 
     def __init__(self, project, config):

dvc/remote/s3.py

@@ -1,9 +1,13 @@
 import os
 import math
-import boto3
 import threading
 import posixpath
 
+try:
+    import boto3
+except ImportError:
+    boto3 = None
+
 try:
     from urlparse import urlparse
 except ImportError:
@@ -31,6 +35,7 @@ class Callback(object):
 class RemoteS3(RemoteBase):
     scheme = 's3'
     REGEX = r'^s3://(?P<path>.*)$'
+    REQUIRES = RemoteBase.REQUIRES + [boto3]
     PARAM_ETAG = 'etag'
 
     def __init__(self, project, config):

dvc/remote/ssh.py

@@ -3,9 +3,13 @@ import re
 import errno
 import getpass
 import filecmp
-import paramiko
 import posixpath
 
+try:
+    import paramiko
+except ImportError:
+    paramiko = None
+
 from dvc.logger import Logger
 from dvc.utils import copyfile, file_md5
 from dvc.progress import progress
@@ -41,6 +45,7 @@ class RemoteSSH(RemoteBase):
     #NOTE: temporarily only absolute paths are allowed
     REGEX = r'^ssh://((?P<user>.*)@)?(?P<host>[^/]*):(?P<path>/.*)$'
 
+    REQUIRES = RemoteBase.REQUIRES + [paramiko]
     PARAM_MD5 = 'md5'
 
     def __init__(self, project, config):

setup.py

@@ -5,6 +5,7 @@ from dvc import VERSION
 
 
 install_requires = [
+    "ply==3.8", # required by google-gax
     "configparser>=3.5.0",
     "zc.lockfile>=1.2.1",
     "future>=0.16.0",
@@ -27,7 +28,6 @@ install_requires = [
 
 # Extra dependencies for remote integrations
 gs = [
-    "ply==3.8",
     "google-cloud==0.32.0",
 ]
 s3 = [