code: def __on_publish(self, client, userdata, mid):
          # pylint: disable=W0613
          
          try:
              self.__in_flight[mid].set()
          except KeyError:
              pass
docs: A message has been published by a server
  
          :param client: Client that received the message
          :param userdata: User data (unused)
          :param mid: Message ID