revert remove assertions from open

dvc/remote/hdfs.py

@@ -143,6 +143,8 @@ class RemoteHDFS(RemoteBASE):
 
     @contextmanager
     def open(self, path_info, mode="r", encoding=None):
+        assert mode in {"r", "rt", "rb"}
+
         try:
             with self.hdfs(path_info) as hdfs, closing(
                 hdfs.open(path_info.path, mode="rb")

dvc/repo/__init__.py

@@ -440,8 +440,6 @@ class Repo(object):
     @contextmanager
     def open(self, path, remote=None, mode="r", encoding=None):
         """Opens a specified resource as a file descriptor"""
-        assert mode in {"r", "rt", "rb"}
-
         try:
             with self._open(path, remote, mode, encoding) as fd:
                 yield fd

dvc/utils/http.py

@@ -13,6 +13,8 @@ def open_url(url, mode="r", encoding=None):
     Resumes on connection error.
     Url could be a string or a callable returning a string.
     """
+    assert mode in {"r", "rt", "rb"}
+
     with iter_url(url) as (response, it):
         bytes_stream = IterStream(it)