Python functools.partial

    def declare_consumer(self, consumer_cls, topic, callback):
        """Create a Consumer using the class that was passed in and
        add it to our list of consumers
        """

        def _connect_error(exc):
            log_info = {‘topic‘: topic, ‘err_str‘: str(exc)}
            LOG.error(_("Failed to declare consumer for topic ‘%(topic)s‘: "
                      "%(err_str)s") % log_info)

        def _declare_consumer():
            consumer = consumer_cls(self.conf, self.channel, topic, callback,
                                    six.next(self.consumer_num))
            self.consumers.append(consumer)
            return consumer

        return self.ensure(_connect_error, _declare_consumer)

    def declare_direct_consumer(self, topic, callback):
        """Create a ‘direct‘ queue.
        In nova‘s use, this is generally a msg_id queue used for
        responses for call/multicall
        """
        self.declare_consumer(DirectConsumer, topic, callback)

    def declare_topic_consumer(self, topic, callback=None, queue_name=None,
                               exchange_name=None):
        """Create a ‘topic‘ consumer."""
        self.declare_consumer(functools.partial(TopicConsumer,
                                                name=queue_name,
                                                exchange_name=exchange_name,
                                                ),
                              topic, callback)

    def declare_fanout_consumer(self, topic, callback):
        """Create a ‘fanout‘ consumer."""
        self.declare_consumer(FanoutConsumer, topic, callback)

functools.partial可以提供对象的默认参数而生成一个新的访问形式，方便统一代码调用形式。以上代码中TopicConsumer类和FanoutConsumer类及DirectConsumer类的构造函数存在差异，如果不使用functools则需要在declare_consumer中进行判断

Python functools.partial