old_contents: from abc import abstractmethod
  from flow.interfaces import IHandler
  from twisted.internet import defer
  
  import logging
  
  
  LOG = logging.getLogger(__name__)
  
  
  class Handler(IHandler):
      def __call__(self, message):
          """
          Returns a deferred that will callback when the message has been
          completely handled, or will errback when the message cannot be
          handled.
          """
          return self._handle_message(message)
  
      @abstractmethod
      def _handle_message(self, message):
          """
          Returns a deferred to __call__
          """
  
new_contents: from abc import abstractmethod
  from flow.interfaces import IHandler
  from twisted.internet import defer
  
  import logging
  
  
  LOG = logging.getLogger(__name__)
  
  
  class Handler(IHandler):
      def __call__(self, message):
          """
          Returns a deferred that will callback when the message has been
          completely handled, or will errback when the message cannot be
          handled.
          """
          return self._handle_message(message)
  
      @abstractmethod
      def _handle_message(self, message):
          """
          Returns a deferred to __call__
          """
  
      def __repr__(self):
          return "%s(queue_name=%s)" % (self.__class__.__name__, self.queue_name)
  
subject: Add __repr__ for handler