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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 stream(self):
        '''
        Return the current zmqstream, creating one if necessary
        '''
        if not hasattr(self, '_stream'):
            self._stream = zmq.eventloop.zmqstream.ZMQStream(self._socket, io_loop=self.io_loop)
        return self._stream