code: def no_route(arg=None):
      
      def wrapper(fn):
          setattr(fn, NO_ROUTES_ATTR, True)
          return fn
  
      if callable(arg):
          return wrapper(arg)
      return wrapper
docs: Decorator to mark a
      :class:`~flask_unchained.bundles.controller.controller.Controller` or
      :class:`~flask_unchained.bundles.resource.resource.Resource` method as *not*
      a route. For example::
  
          class SiteController(Controller):
              @route('/')
              def index():
                  return self.render('index')
  
              def about():
                  return self.render('about', stuff=self.utility_method())
  
              @no_route
              def utility_method():
                  return 'stuff'
  
          # registered like so in ``your_app_bundle/routes.py``
          routes = lambda: [
              controller(SiteController),
          ]
  
          # results in the following routes
          SiteController.index            => GET /
          SiteController.about            => GET /about
  
          # but without the @no_route decorator, it would have also added this route:
          SiteController.utility_method   => GET /utility-method
  
      NOTE: The perhaps more Pythonic way to accomplish is simply to make all non-route
      methods protected by prefixing them with an underscore, eg ``_utility_method``.