def startService(self):
        """
        Start listening on the endpoint, unless L{privilegedStartService} got
        around to it already.
        """
        service.Service.startService(self)
        if self._waitingForPort is None:
            self.privilegedStartService()

        Start listening on the endpoint, unless L{privilegedStartService} got
        around to it already.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/internet.py