def handle_WELCOME(self, line):
        """
        Handle a server response which is expected to be a server greeting.

        @type line: L{bytes}
        @param line: A received line.
        """
        code, data = line.split(b' ', 1)
        if code != b'+OK':
            self.transport.loseConnection()
        else:
            m = self.welcomeRe.match(line)
            if m:
                self.welcomeCode = m.group(1)

        Handle a server response which is expected to be a server greeting.

        @type line: L{bytes}
        @param line: A received line.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/pop3.py