code: def get_action_handler(self, controller_name, action_name):
          
          try_actions = [
              controller_name + '/' + action_name,
              controller_name + '/not_found',
              # call Index controller to catch all unhandled pages
              'index/not_found'
          ]
          # search first appropriate action handler
          for path in try_actions:
              if path in self._controllers:
                  return self._controllers[path]
          return None
docs: Return action of controller as callable.
  
          If requested controller isn't found - return 'not_found' action
          of requested controller or Index controller.