code: def _declare_consumer(self, consumer, nowait=False):
          
          if consumer.queue not in self._open_consumers:
              # Use the ConsumerSet's consumer by default, but if the
              # child consumer has a callback, honor it.
              callback = consumer.callbacks and \
                  consumer._receive_callback or self._receive_callback
              self.backend.declare_consumer(queue=consumer.queue,
                                            no_ack=consumer.no_ack,
                                            nowait=nowait,
                                            callback=callback,
                                            consumer_tag=consumer.consumer_tag)
              self._open_consumers[consumer.queue] = consumer.consumer_tag
docs: Declare consumer so messages can be received from it using
          :meth:`iterconsume`.