code: def wsgi_extend(self, controller):
          
  
          # Add/override actions
          for key, action in controller.wsgi_actions.items():
              # If it's a new action, we'll need to route
              if self.wsgi_mapper and key not in self.wsgi_actions:
                  self._route(key, action)
  
              self.wsgi_actions[key] = action
  
              # Clear existing action descriptors
              self.wsgi_descriptors.pop(key, None)
  
          # Register extensions
          for key, extensions in controller.wsgi_extensions.items():
              # Skip empty extension lists
              if not extensions:
                  continue
  
              # Prime the pump...
              self.wsgi_extensions.setdefault(key, [])
  
              # Add the extensions
              self.wsgi_extensions[key].extend(extensions)
  
              # Clear existing action descriptors
              self.wsgi_descriptors.pop(key, None)
docs: Extends a controller by registering another controller as an
          extension of it.  All actions defined on the extension
          controller have routes generated for them (only if none
          already exist) and are made actions of this controller; all
          extensions defined on the extension controller are added to
          the extensions registered on this controller.