Invoke view functions with kwargs instead of positional args

Closes #429.

CHANGELOG.rst

@@ -5,6 +5,14 @@ CHANGELOG
 1.0.0b2
 =======
 
+Please read the `upgrade notes for 1.0.0b2
+<http://chalice.readthedocs.io/en/latest/upgrading.html#v1-0-0b2>`__
+for more detailed information about upgrading to this release.
+
+Note: to install this beta version of chalice you must specify
+``pip install 'chalice>=1.0.0b2,<2.0.0'`` or
+use the ``--pre`` flag for pip: ``pip install --pre chalice``.
+
 * Set env vars from config in ``chalice local``
   (`#396 <https://github.com/awslabs/chalice/issues/396>`__)
 * Fix edge case when building packages with optional c extensions
@@ -16,6 +24,9 @@ CHANGELOG
   (`#428 <https://github.com/awslabs/chalice/pull/428>`__)
 * Validate route path is not an empty string
   (`#432 <https://github.com/awslabs/chalice/pull/432>`__)
+* Change route code to invoke view function with kwargs instead of
+  positional args
+  (`#429 <https://github.com/awslabs/chalice/issues/429>`__)
 
 
 1.0.0b1

chalice/app.py

@@ -568,8 +568,8 @@ def __call__(self, event, context):
                 http_status_code=405)
         route_entry = self.routes[resource_path][http_method]
         view_function = route_entry.view_function
-        function_args = [event['pathParameters'][name]
-                         for name in route_entry.view_args]
+        function_args = {name: event['pathParameters'][name]
+                         for name in route_entry.view_args}
         self.current_request = Request(event['queryStringParameters'],
                                        event['headers'],
                                        event['pathParameters'],
@@ -631,7 +631,7 @@ def _validate_binary_response(self, request_headers, response_headers):
 
     def _get_view_function_response(self, view_function, function_args):
         try:
-            response = view_function(*function_args)
+            response = view_function(**function_args)
             if not isinstance(response, Response):
                 response = Response(body=response)
             self._validate_response(response)

docs/source/topics/routing.rst

@@ -57,8 +57,8 @@ will then be passed in as arguments to your view function:
 
 If you then go to ``https://endpoint/users/james``, then the view function
 will be called as: ``users('james')``.  The parameters are passed as
-positional parameters based on the order they appear in the URL. The argument
-names for the view function do not need to match the name of the captured
+keyword parameters based on the name as they appear in the URL. The argument
+names for the view function must match the name of the captured
 argument:
 
 
@@ -70,8 +70,8 @@ argument:
 
 
     @app.route('/a/{first}/b/{second}')
-    def users(first_arg, second_arg):
-        return {'first': first_arg, 'second': second_arg}
+    def users(first, second):
+        return {'first': first, 'second': second}
 
 
 Other Request Metadata

docs/source/upgrading.rst

@@ -7,6 +7,46 @@ interested in the high level changes, see the
 `CHANGELOG.rst <https://github.com/awslabs/chalice/blob/master/CHANGELOG.rst>`__)
 file.
 
+.. _v1-0-0b2:
+
+1.0.0b2
+-------
+
+The url parameter names and the function argument names must match.
+Previously, the routing code would use positional args ``handler(*args)``
+to invoke a view function.  In this version, kwargs are now used instead:
+``handler(**view_args)``.  For example, this code will no longer work:
+
+.. code-block:: python
+
+    @app.route('/{a}/{b}')
+    def myview(first, second)
+        return {}
+
+
+The example above must be updated to:
+
+
+.. code-block:: python
+
+    @app.route('/{a}/{b}')
+    def myview(a, b)
+        return {}
+
+Now that functions are invoked with kwargs, the order doesn't matter.  You may
+also write the above view function as:
+
+
+.. code-block:: python
+
+    @app.route('/{a}/{b}')
+    def myview(b, a)
+        return {}
+
+
+This was done to have consistent behavior with other web frameworks such as
+Flask.
+
 .. _v1-0-0b1:
 
 1.0.0b1

tests/unit/test_app.py

@@ -1172,3 +1172,16 @@ def test_aws_execution_env_set():
     assert env['AWS_EXECUTION_ENV'] == (
         'AWS_Lambda_python2.7 aws-chalice/%s' % chalice_version
     )
+
+
+def test_can_use_out_of_order_args():
+    demo = app.Chalice('demo-app')
+
+    # Note how the url params and function args are out of order.
+    @demo.route('/{a}/{b}', methods=['GET'])
+    def index(b, a):
+        return {'a': a, 'b': b}
+    event = create_event('/{a}/{b}', 'GET', {'a': 'first', 'b': 'second'})
+    response = demo(event, context=None)
+    response = json_response_body(response)
+    assert response == {'a': 'first', 'b': 'second'}