def runReactorWithLogging(config, oldstdout, oldstderr, profiler=None,
                          reactor=None):
    """
    Start the reactor, using profiling if specified by the configuration, and
    log any error happening in the process.

    @param config: configuration of the twistd application.
    @type config: L{ServerOptions}

    @param oldstdout: initial value of C{sys.stdout}.
    @type oldstdout: C{file}

    @param oldstderr: initial value of C{sys.stderr}.
    @type oldstderr: C{file}

    @param profiler: object used to run the reactor with profiling.
    @type profiler: L{AppProfiler}

    @param reactor: The reactor to use.  If L{None}, the global reactor will
        be used.
    """
    if reactor is None:
        from twisted.internet import reactor
    try:
        if config['profile']:
            if profiler is not None:
                profiler.run(reactor)
        elif config['debug']:
            sys.stdout = oldstdout
            sys.stderr = oldstderr
            if runtime.platformType == 'posix':
                signal.signal(signal.SIGUSR2, lambda *args: pdb.set_trace())
                signal.signal(signal.SIGINT, lambda *args: pdb.set_trace())
            fixPdb()
            pdb.runcall(reactor.run)
        else:
            reactor.run()
    except:
        close = False
        if config['nodaemon']:
            file = oldstdout
        else:
            file = open("TWISTD-CRASH.log", "a")
            close = True
        try:
            traceback.print_exc(file=file)
            file.flush()
        finally:
            if close:
                file.close()

    Start the reactor, using profiling if specified by the configuration, and
    log any error happening in the process.

    @param config: configuration of the twistd application.
    @type config: L{ServerOptions}

    @param oldstdout: initial value of C{sys.stdout}.
    @type oldstdout: C{file}

    @param oldstderr: initial value of C{sys.stderr}.
    @type oldstderr: C{file}

    @param profiler: object used to run the reactor with profiling.
    @type profiler: L{AppProfiler}

    @param reactor: The reactor to use.  If L{None}, the global reactor will
        be used.
    
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/app.py