def _getLogObserver(self):
        """
        Create and return a suitable log observer for the given configuration.

        The observer will go to syslog using the prefix C{_syslogPrefix} if
        C{_syslog} is true.  Otherwise, it will go to the file named
        C{_logfilename} or, if C{_nodaemon} is true and C{_logfilename} is
        C{"-"}, to stdout.

        @return: An object suitable to be passed to C{log.addObserver}.
        """
        if self._syslog:
            from twisted.python import syslog
            return syslog.SyslogObserver(self._syslogPrefix).emit

        if self._logfilename == '-':
            if not self._nodaemon:
                sys.exit('Daemons cannot log to stdout, exiting!')
            logFile = sys.stdout
        elif self._nodaemon and not self._logfilename:
            logFile = sys.stdout
        else:
            if not self._logfilename:
                self._logfilename = 'twistd.log'
            logFile = logfile.LogFile.fromFullPath(self._logfilename)
            try:
                import signal
            except ImportError:
                pass
            else:
                # Override if signal is set to None or SIG_DFL (0)
                if not signal.getsignal(signal.SIGUSR1):
                    def rotateLog(signal, frame):
                        from twisted.internet import reactor
                        reactor.callFromThread(logFile.rotate)
                    signal.signal(signal.SIGUSR1, rotateLog)
        return logger.textFileLogObserver(logFile)

        Create and return a suitable log observer for the given configuration.

        The observer will go to syslog using the prefix C{_syslogPrefix} if
        C{_syslog} is true.  Otherwise, it will go to the file named
        C{_logfilename} or, if C{_nodaemon} is true and C{_logfilename} is
        C{"-"}, to stdout.

        @return: An object suitable to be passed to C{log.addObserver}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/scripts/_twistd_unix.py