def state_SHORT(self, line):
        """
        Handle server responses for the SHORT state in which the server is
        expected to send a single line response.

        Parse the response and fire the deferred which is waiting on receipt of
        a complete response.  Transition the state back to WAITING.

        @type line: L{bytes}
        @param line: A line received from the server.

        @rtype: L{bytes}
        @return: The next state.
        """
        deferred, self._waiting = self._waiting, None
        self._unblock()
        code, status = _codeStatusSplit(line)
        if code == OK:
            deferred.callback(status)
        else:
            deferred.errback(ServerErrorResponse(status))
        return 'WAITING'

        Handle server responses for the SHORT state in which the server is
        expected to send a single line response.

        Parse the response and fire the deferred which is waiting on receipt of
        a complete response.  Transition the state back to WAITING.

        @type line: L{bytes}
        @param line: A line received from the server.

        @rtype: L{bytes}
        @return: The next state.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/pop3client.py