Allow pushing a single tag.

Closes #282

README.md

@@ -201,7 +201,7 @@ c.pull(repository, tag=None, stream=False)
 Identical to the `docker pull` command.
 
 ```python
-c.push(repository, stream=False)
+c.push(repository, tag=None, stream=False)
 ```
 
 Identical to the `docker push` command.

docker/client.py

@@ -747,9 +747,14 @@ class Client(requests.Session):
         else:
             return self._result(response)
 
-    def push(self, repository, stream=False):
+    def push(self, repository, tag=None, stream=False):
+        if not tag:
+            repository, tag = utils.parse_repository_tag(repository)
         registry, repo_name = auth.resolve_repository_name(repository)
         u = self._url("/images/{0}/push".format(repository))
+        params = {
+            'tag': tag
+        }
         headers = {}
 
         if utils.compare_version('1.5', self._version) >= 0:
@@ -765,9 +770,10 @@ class Client(requests.Session):
             if authcfg:
                 headers['X-Registry-Auth'] = auth.encode_header(authcfg)
 
-            response = self._post_json(u, None, headers=headers, stream=stream)
+            response = self._post_json(u, None, headers=headers,
+                                       stream=stream, params=params)
         else:
-            response = self._post_json(u, None, stream=stream)
+            response = self._post_json(u, None, stream=stream, params=params)
 
         return stream and self._stream_helper(response) \
             or self._result(response)

tests/test.py

@@ -1306,6 +1306,28 @@ class DockerClientTest(Cleanup, unittest.TestCase):
 
         fake_request.assert_called_with(
             url_prefix + 'images/test_image/push',
+            params={
+                'tag': None
+            },
+            data='{}',
+            headers={'Content-Type': 'application/json'},
+            stream=False,
+            timeout=docker.client.DEFAULT_TIMEOUT_SECONDS
+        )
+
+    def test_push_image_with_tag(self):
+        try:
+            with mock.patch('docker.auth.auth.resolve_authconfig',
+                            fake_resolve_authconfig):
+                self.client.push(fake_api.FAKE_IMAGE_NAME, tag=fake_api.FAKE_TAG_NAME)
+        except Exception as e:
+            self.fail('Command should not raise exception: {0}'.format(e))
+
+        fake_request.assert_called_with(
+            url_prefix + 'images/test_image/push',
+            params={
+                'tag': fake_api.FAKE_TAG_NAME,
+            },
             data='{}',
             headers={'Content-Type': 'application/json'},
             stream=False,
@@ -1322,6 +1344,9 @@ class DockerClientTest(Cleanup, unittest.TestCase):
 
         fake_request.assert_called_with(
             url_prefix + 'images/test_image/push',
+            params={
+                'tag': None
+            },
             data='{}',
             headers={'Content-Type': 'application/json'},
             stream=True,