code: def is_outbound_message_filter(cb):
      
  
      try:
          handlers = get_magic_attr(cb)
      except AttributeError:
          return False
  
      hs = HandlerSpec(
          (_apply_outbound_message_filter, ())
      )
  
      return hs in handlers
docs: Return true if `cb` has been decorated with
      :func:`outbound_message_filter`.