Add Flask.config_class feature

flask/app.py

@@ -175,6 +175,15 @@ class Flask(_PackageBoundObject):
                                      _set_request_globals_class)
     del _get_request_globals_class, _set_request_globals_class
 
+    #: The class that is used for the ``config`` attribute of this app.
+    #: Defaults to :class:`~flask.Config`.
+    #:
+    #: Example use cases for a custom class:
+    #:
+    #: 1. Default values for certain config options.
+    #: 2. Access to config values through attributes in addition to keys.
+    config_class = Config
+
     #: The debug flag.  Set this to `True` to enable debugging of the
     #: application.  In debug mode the debugger will kick in when an unhandled
     #: exception occurs and the integrated server will automatically reload
@@ -609,7 +618,7 @@ class Flask(_PackageBoundObject):
         root_path = self.root_path
         if instance_relative:
             root_path = self.instance_path
-        return Config(root_path, self.default_config)
+        return self.config_class(root_path, self.default_config)
 
     def auto_find_instance_path(self):
         """Tries to locate the instance path if it was not provided to the

flask/testsuite/__init__.py

@@ -157,6 +157,9 @@ class FlaskTestCase(unittest.TestCase):
     def assert_not_in(self, x, y):
         self.assertNotIn(x, y)
 
+    def assert_isinstance(self, obj, cls):
+        self.assertIsInstance(obj, cls)
+
     if sys.version_info[:2] == (2, 6):
         def assertIn(self, x, y):
             assert x in y, "%r unexpectedly not in %r" % (x, y)

flask/testsuite/config.py

@@ -99,6 +99,16 @@ class ConfigTestCase(FlaskTestCase):
             self.assert_true(0, 'expected config')
         self.assert_false(app.config.from_pyfile('missing.cfg', silent=True))
 
+    def test_custom_config_class(self):
+        class Config(flask.Config):
+            pass
+        class Flask(flask.Flask):
+            config_class = Config
+        app = Flask(__name__)
+        self.assert_isinstance(app.config, Config)
+        app.config.from_object(__name__)
+        self.common_object_test(app)
+
     def test_session_lifetime(self):
         app = flask.Flask(__name__)
         app.config['PERMANENT_SESSION_LIFETIME'] = 42