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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 _process_ping(self):
 """ The server will be periodically sending a PING, and if the the client does not reply a PONG back a number of times, it will close the connection sending an `-ERR 'Stale Connection'` error. """

        yield self.send_command(PONG_PROTO)
        if self._flush_queue.empty():
            yield self._flush_pending()