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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 _send_frame(self, connection, frame):
 """ Sends a frame to a specific subscriber connection. (This method assumes it is being called from within a lock-guarded public method.) @param connection: The subscriber connection object to send to. @type connection: L{coilmq.server.StompConnection} @param frame: The frame to send. @type frame: L{stompclient.frame.Frame} """

        assert connection is not None
        assert frame is not None

        self.log.debug("Delivering frame %s to connection %s" %
                       (frame, connection))

        if connection.reliable_subscriber:
            if connection in self._pending:
                raise RuntimeError("Connection already has a pending frame.")
            self.log.debug(
                "Tracking frame %s as pending for connection %s" % (frame, connection))
            self._pending[connection] = frame

        connection.send_frame(frame)