Enforce passing string as version param in ctor

docker/client.py

@@ -50,6 +50,12 @@ class Client(requests.Session):
             raise errors.TLSParameterError(
                 'If using TLS, the base_url argument must begin with '
                 '"https://".')
+        if not isinstance(version, six.string_types):
+            raise errors.DockerException(
+                'version parameter must be a string. Found {0}'.format(
+                    type(version).__name__
+                )
+            )
         self.base_url = base_url
         self._version = version
         self._timeout = timeout

tests/test.py

@@ -102,6 +102,17 @@ class DockerClientTest(Cleanup, unittest.TestCase):
     def tearDown(self):
         self.client.close()
 
+    def test_ctor(self):
+        try:
+            docker.Client(version=1.12)
+        except Exception as e:
+            self.assertTrue(isinstance(e, docker.errors.DockerException))
+            if not six.PY3:
+                self.assertEqual(
+                    e.message,
+                    'version parameter must be a string. Found float'
+                )
+
     #########################
     #   INFORMATION TESTS   #
     #########################