def startLogging(self):
        """
        Start the L{twisted.logger} logging system.
        """
        logFile = self._logFile

        fileLogObserverFactory = self._fileLogObserverFactory

        fileLogObserver = fileLogObserverFactory(logFile)

        logLevelPredicate = LogLevelFilterPredicate(
            defaultLogLevel=self._defaultLogLevel
        )

        filteringObserver = FilteringLogObserver(
            fileLogObserver, [logLevelPredicate]
        )

        globalLogBeginner.beginLoggingTo([filteringObserver])

        Start the L{twisted.logger} logging system.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/runner/_runner.py