Question

I would like to define routes on my RequestHandler objects by decorating them rather than providing the application with a list when it is created.

My WSGIApplication is defined as follows:

class WSGIApplication(webapp2.WSGIApplication):
    def __init__(self, *args, **kwargs):
        super(WSGIApplication, self).__init__(*args, **kwargs)
        self.router.set_dispatcher(self.__class__.custom_dispatcher)

    @staticmethod
    def custom_dispatcher(router, request, response):
        rv = router.default_dispatcher(request, response)
        if isinstance(rv, basestring):
            rv = webapp2.Response(rv)
        elif isinstance(rv, tuple):
            rv = webapp2.Response(*rv)

        return rv

    def route(self, url, name):
        def outer_wrapped(cls):
            logging.info("Adding route %s to class %s with name %s"
                         % (url, cls, name))
            self.router.add(RedirectRoute(url, cls,
                                          name=name,
                                          strict_slash=True))
            return cls
        return outer_wrapped

in package.utils

And I have my application defined in package.application

app.yaml has

application: theapplication
version: 1
runtime: python27
api_version: 1
threadsafe: yes

handlers:
- url: .*
  script: package.main.application
  secure: always

package.main is as follows:

from package.application import application
from package.pages import pages

package.application is as follows (with the secret key hashed out):

from package import utils

conf = {}
conf['webapp2_extras.sessions'] = {'secret_key':
    """##############################################"""}

application = utils.WSGIApplication([], config=conf)

and here are a couple of handlers from package.pages:

from package.application import application as app


@app.route('/conversations', 'view_messages')
class Messages(BaseHandler):
    @users.require_login
    def get(self):
        conversations = self.current_user.get_user_conversations()
        return self.render('conversations.slim', conversations=conversations)


@app.route('/', 'index')
class Index(BaseHandler):
    def get(self):
        return self.render('index.slim')

The index page works fine, everything else 404s, the log simply says:

INFO     2012-07-23 14:23:46,258 __init__.py:26] /notifications
INFO     2012-07-23 14:23:46,272 dev_appserver.py:2952] "GET /notifications HTTP/1.1" 404 -

I presume this is caused in some way by appengine’s import caching preventing the decorators from ever being run and adding themselves to the app.

Of course I fell prey to the trap of assuming I had any clue of what was causing the problem. I added further logging statements to output the list of routes before attempting each dispatch and I find that all of the routes are in the router as one would expect:

    ...
    def custom_dispatcher(router, request, response):
        logging.info(router.match_routes)
        logging.info(router.build_routes)
        rv = router.default_dispatcher(request, response)
    ...

With the following log output on pointing my browser to /conversations:

INFO     2012-08-04 13:16:40,513 utils.py:13] [<Route('/friendship', <class 'package.pages.pages.Friendship'>, name='friendship', defaults={}, build_only=False)>, <Route('/friendship/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/friendship', <class 'package.pages.pages.Friendship'>, name='friendship', defaults={}, build_only=False)>>, '_name': 'friendship'}, build_only=False)>, <Route('/signup', <class 'package.pages.pages.Signup'>, name='signup', defaults={}, build_only=False)>, <Route('/signup/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/signup', <class 'package.pages.pages.Signup'>, name='signup', defaults={}, build_only=False)>>, '_name': 'signup'}, build_only=False)>, <Route('/preferences', <class 'package.pages.pages.UserPage'>, name='user_prefs', defaults={}, build_only=False)>, <Route('/preferences/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/preferences', <class 'package.pages.pages.UserPage'>, name='user_prefs', defaults={}, build_only=False)>>, '_name': 'user_prefs'}, build_only=False)>, <Route('/<username:[a-zA-Z]+>', <class 'package.pages.pages.UserPage'>, name='user_page', defaults={}, build_only=False)>, <Route('/<username:[a-zA-Z]+>/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/<username:[a-zA-Z]+>', <class 'package.pages.pages.UserPage'>, name='user_page', defaults={}, build_only=False)>>, '_name': 'user_page'}, build_only=False)>, <Route('/message', <class 'package.pages.pages.SendMessagePage'>, name='send_message', defaults={}, build_only=False)>, <Route('/message/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/message', <class 'package.pages.pages.SendMessagePage'>, name='send_message', defaults={}, build_only=False)>>, '_name': 'send_message'}, build_only=False)>, <Route('/conversations', <class 'package.pages.pages.Messages'>, name='view_messages', defaults={}, build_only=False)>, <Route('/conversations/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/conversations', <class 'package.pages.pages.Messages'>, name='view_messages', defaults={}, build_only=False)>>, '_name': 'view_messages'}, build_only=False)>, <Route('/conversation/<conversation_id>', <class 'package.pages.pages.ConversationPage'>, name='conversation', defaults={}, build_only=False)>, <Route('/conversation/<conversation_id>/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/conversation/<conversation_id>', <class 'package.pages.pages.ConversationPage'>, name='conversation', defaults={}, build_only=False)>>, '_name': 'conversation'}, build_only=False)>, <Route('/boards', <class 'package.pages.pages.Boards'>, name='view_boards', defaults={}, build_only=False)>, <Route('/boards/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/boards', <class 'package.pages.pages.Boards'>, name='view_boards', defaults={}, build_only=False)>>, '_name': 'view_boards'}, build_only=False)>, <Route('/boards/<board>', <class 'package.pages.pages.BoardPage'>, name='view_board', defaults={}, build_only=False)>, <Route('/boards/<board>/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/boards/<board>', <class 'package.pages.pages.BoardPage'>, name='view_board', defaults={}, build_only=False)>>, '_name': 'view_board'}, build_only=False)>, <Route('/boards/<board>/new_thread', <class 'package.pages.pages.NewThreadPage'>, name='new_thread', defaults={}, build_only=False)>, <Route('/boards/<board>/new_thread/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/boards/<board>/new_thread', <class 'package.pages.pages.NewThreadPage'>, name='new_thread', defaults={}, build_only=False)>>, '_name': 'new_thread'}, build_only=False)>, <Route('/notifications', <class 'package.pages.pages.Notifications'>, name='notifications', defaults={}, build_only=False)>, <Route('/notifications/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/notifications', <class 'package.pages.pages.Notifications'>, name='notifications', defaults={}, build_only=False)>>, '_name': 'notifications'}, build_only=False)>, <Route('/img/<blob_key>', <class 'package.pages.pages.DisplayImagePage'>, name='display_image', defaults={}, build_only=False)>, <Route('/img/<blob_key>/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/img/<blob_key>', <class 'package.pages.pages.DisplayImagePage'>, name='display_image', defaults={}, build_only=False)>>, '_name': 'display_image'}, build_only=False)>, <Route('/', <class 'package.pages.pages.Index'>, name='index', defaults={}, build_only=False)>, <Route('/', <class 'webapp2.RedirectHandler'>, name=None, defaults={'_uri': <bound method RedirectRoute._redirect of <Route('/', <class 'package.pages.pages.Index'>, name='index', defaults={}, build_only=False)>>, '_name': 'index'}, build_only=False)>]
INFO     2012-08-04 13:16:40,513 utils.py:14] {'index': <Route('/', <class 'package.pages.pages.Index'>, name='index', defaults={}, build_only=False)>, 'view_boards': <Route('/boards', <class 'package.pages.pages.Boards'>, name='view_boards', defaults={}, build_only=False)>, 'notifications': <Route('/notifications', <class 'package.pages.pages.Notifications'>, name='notifications', defaults={}, build_only=False)>, 'friendship': <Route('/friendship', <class 'package.pages.pages.Friendship'>, name='friendship', defaults={}, build_only=False)>, 'signup': <Route('/signup', <class 'package.pages.pages.Signup'>, name='signup', defaults={}, build_only=False)>, 'view_messages': <Route('/conversations', <class 'package.pages.pages.Messages'>, name='view_messages', defaults={}, build_only=False)>, 'conversation': <Route('/conversation/<conversation_id>', <class 'package.pages.pages.ConversationPage'>, name='conversation', defaults={}, build_only=False)>, 'send_message': <Route('/message', <class 'package.pages.pages.SendMessagePage'>, name='send_message', defaults={}, build_only=False)>, 'new_thread': <Route('/boards/<board>/new_thread', <class 'package.pages.pages.NewThreadPage'>, name='new_thread', defaults={}, build_only=False)>, 'view_board': <Route('/boards/<board>', <class 'package.pages.pages.BoardPage'>, name='view_board', defaults={}, build_only=False)>, 'display_image': <Route('/img/<blob_key>', <class 'package.pages.pages.DisplayImagePage'>, name='display_image', defaults={}, build_only=False)>, 'user_prefs': <Route('/preferences', <class 'package.pages.pages.UserPage'>, name='user_prefs', defaults={}, build_only=False)>, 'user_page': <Route('/<username:[a-zA-Z]+>', <class 'package.pages.pages.UserPage'>, name='user_page', defaults={}, build_only=False)>}
INFO     2012-08-04 13:16:40,515 __init__.py:26] /conversations
INFO     2012-08-04 13:16:40,533 dev_appserver.py:2952] "GET /conversations HTTP/1.1" 404 -
INFO     2012-08-04 13:16:40,626 dev_appserver.py:2952] "GET /favicon.ico HTTP/1.1" 200 -

What on earth am I failing to notice?

Answer 1

I had a route that was overriding all the other routes but raising a 404 on them (/username leads to a user page; there’s no user called “conversations”). I had forgotten to make this route have lowest priority in the switch to the decorator routing method.

I figured this out by first building a minimal application using the same routing method to see that it worked just fine on app engine. Then I caught HTTPNotFound exceptions in my handler and printed a stack trace when they occurred; this made it pretty clear that it was a line in the get method of my user page class throwing a 404 intentionally then the problems was fairly obvious.