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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 _create_sending_stream(self, pub_addr):
 """ Create a `ZMQStream` for sending responses back to Mongrel2. """

        sock = self._zmq_context.socket(zmq.PUB)
        sock.setsockopt(zmq.IDENTITY, self.sender_id)
        sock.connect(pub_addr)
        stream = ZMQStream(sock, io_loop=self.io_loop)

        return stream