def main(): app = QApplicationMessaging(sys.argv) if app.isRunning(): if len(sys.argv) > 1: app.sendMessage(sys.argv[1]) else: app.sendMessage('ARISE') else: main = MainWindow(app) main.setWindowIcon(QIcon(':/favicon.png')) app.aboutToQuit.connect(main.cleanUp) app.setActiveWindow(main) main.show() sys.exit(app.exec_())