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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sub(self, topics=(b'',)):
 """ Returns an iterable that can be used to iterate over incoming messages, that were published with one of the topics specified in ``topics``. Note that the iterable returns as many parts as sent by subscribed publishers. :param topics: a list of topics to subscribe to (default=b'') :type topics: list of bytes :rtype: generator """

        sock = self.__sock(zmq.SUB)

        for topic in topics:
            if not isinstance(topic, bytes):
                error = 'Topics must be a list of bytes'
                log.error(error)
                raise TypeError(error)
            sock.setsockopt(zmq.SUBSCRIBE, topic)

        return self.__recv_generator(sock)