def state_LONG_INITIAL(self, line):
        """
        Handle server responses for the LONG_INITIAL state in which the server
        is expected to send the first line of a multi-line response.

        Parse the response.  On an OK response, transition the state to
        LONG.  On an ERR response, cleanup and transition the state to
        WAITING.

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

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

        Handle server responses for the LONG_INITIAL state in which the server
        is expected to send the first line of a multi-line response.

        Parse the response.  On an OK response, transition the state to
        LONG.  On an ERR response, cleanup and transition the state 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