code: def start_consuming(self):
          
          self._logger.info('Issuing consumer related RPC commands')
          self.add_on_cancel_callback()
          self._consumer_tag = self._channel.basic_consume(self.on_message,
                                                           self._queue)
docs: This method sets up the consumer by first calling
          add_on_cancel_callback so that the object is notified if RabbitMQ
          cancels the consumer. It then issues the Basic.Consume RPC command
          which returns the consumer tag that is used to uniquely identify the
          consumer with RabbitMQ. We keep the value to use it when we want to
          cancel consuming. The on_message method is passed in as a callback pika
          will invoke when a message is fully received.