Ensure default timeout is used by API Client

The `from_env` method on the `docker` module passed `None` as the
value for the `timeout` keyword argument which overrode the default
value in the initialiser, taken from `constants` module.

This sets the default in the initialiser to `None` and adds logic
to set that, in the same way that `version` is handled.
Signed-off-by: grahamlyons <graham@grahamlyons.com>

docker/api/client.py

@@ -83,8 +83,7 @@ class APIClient(
             configuration.
         user_agent (str): Set a custom user agent for requests to the server.
     """
-    def __init__(self, base_url=None, version=None,
-                 timeout=DEFAULT_TIMEOUT_SECONDS, tls=False,
+    def __init__(self, base_url=None, version=None, timeout=None, tls=False,
                  user_agent=DEFAULT_USER_AGENT, num_pools=DEFAULT_NUM_POOLS):
         super(APIClient, self).__init__()
 
@@ -94,7 +93,11 @@ class APIClient(
             )
 
         self.base_url = base_url
-        self.timeout = timeout
+        if timeout is not None:
+            self.timeout = timeout
+        else:
+            self.timeout = DEFAULT_TIMEOUT_SECONDS
+
         self.headers['User-Agent'] = user_agent
 
         self._auth_configs = auth.load_config()

tests/unit/client_test.py

 import datetime
 import docker
 from docker.utils import kwargs_from_env
+from docker.constants import (
+    DEFAULT_DOCKER_API_VERSION, DEFAULT_TIMEOUT_SECONDS
+)
 import os
 import unittest
 
@@ -96,3 +99,13 @@ class FromEnvTest(unittest.TestCase):
         client = docker.from_env(version='2.32')
         self.assertEqual(client.api.base_url, "https://192.168.59.103:2376")
         self.assertEqual(client.api._version, '2.32')
+
+    def test_from_env_without_version_uses_default(self):
+        client = docker.from_env()
+
+        self.assertEqual(client.api._version, DEFAULT_DOCKER_API_VERSION)
+
+    def test_from_env_without_timeout_uses_default(self):
+        client = docker.from_env()
+
+        self.assertEqual(client.api.timeout, DEFAULT_TIMEOUT_SECONDS)