code: def on_message(self, unused_channel, basic_deliver, properties, body):
          
          _logger.debug('Received message # %s from %s: %s',
                        basic_deliver.delivery_tag, properties.app_id, body)
          if self.ws and body:
              self.messages.append(body)
          _logger.debug('out ws : %s', len(self.ws))
          _logger.debug('out messages : %s', len(self.messages))
          self.acknowledge_message(basic_deliver.delivery_tag)
docs: Invoked by pika when a message is delivered from RabbitMQ. The
          channel is passed for your convenience. The basic_deliver object that
          is passed in carries the exchange, routing key, delivery tag and
          a redelivered flag for the message. The properties passed in is an
          instance of BasicProperties with the message properties and the body
          is the message that was sent.
  
          :param pika.channel.Channel unused_channel: The channel object
          :param pika.Spec.Basic.Deliver: basic_deliver method
          :param pika.Spec.BasicProperties: properties
          :param str|unicode body: The message body