def sendLong(self, command, params):
        """
        Send a POP3 command to which a long response is expected.

        @type command: L{bytes}
        @param command: A POP3 command.

        @type params: stringifyable L{object}
        @param params: Command arguments.
        """
        if params:
            if not isinstance(params, bytes):
                params = str(params).encode("utf-8")
            self.sendLine(command + b' ' + params)
        else:
            self.sendLine(command)
        self.command = command
        self.mode = FIRST_LONG

        Send a POP3 command to which a long response is expected.

        @type command: L{bytes}
        @param command: A POP3 command.

        @type params: stringifyable L{object}
        @param params: Command arguments.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/pop3.py