code: def get_main_app(argv=[]):
      
      app = QApplication(argv)
      app.setApplicationName(__appname__)
      app.setWindowIcon(newIcon("app"))
      # Tzutalin 201705+: Accept extra agruments to change predefined class file
      # Usage : labelImg.py image predefClassFile saveDir
      win = MainWindow(argv[1] if len(argv) >= 2 else None,
                       argv[2] if len(argv) >= 3 else os.path.join(
                           os.path.dirname(sys.argv[0]),
                           'data', 'predefined_classes.txt'),
                       argv[3] if len(argv) >= 4 else None)
      win.show()
      return app, win
docs: Standard boilerplate Qt application code.
      Do everything but app.exec_() -- so that we can test the application in one thread