def opt_debug(self):
        """
        Run the application in the Python Debugger (implies nodaemon),
        sending SIGUSR2 will drop into debugger
        """
        defer.setDebugging(True)
        failure.startDebugMode()
        self['debug'] = True

        Run the application in the Python Debugger (implies nodaemon),
        sending SIGUSR2 will drop into debugger
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/app.py