Add helpful error for APIClient methods on Client

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

docker/client.py

@@ -154,4 +154,14 @@ class Client(object):
         return self.api.version(*args, **kwargs)
     version.__doc__ = APIClient.version.__doc__
 
+    def __getattr__(self, name):
+        s = ["'Client' object has no attribute '{}'".format(name)]
+        # If a user calls a method on APIClient, they
+        if hasattr(APIClient, name):
+            s.append("In docker-py 2.0, this method is now on the object "
+                     "APIClient. See the low-level API section of the "
+                     "documentation for more details.".format(name))
+        raise AttributeError(' '.join(s))
+
+
 from_env = Client.from_env

tests/unit/client_test.py

@@ -45,6 +45,20 @@ class ClientTest(unittest.TestCase):
         assert client.version() == mock_func.return_value
         mock_func.assert_called_with()
 
+    def test_call_api_client_method(self):
+        client = docker.from_env()
+        with self.assertRaises(AttributeError) as cm:
+            client.create_container()
+        s = str(cm.exception)
+        assert "'Client' object has no attribute 'create_container'" in s
+        assert "this method is now on the object APIClient" in s
+
+        with self.assertRaises(AttributeError) as cm:
+            client.abcdef()
+        s = str(cm.exception)
+        assert "'Client' object has no attribute 'abcdef'" in s
+        assert "this method is now on the object APIClient" not in s
+
 
 class FromEnvTest(unittest.TestCase):