Kivy:如何在类外更新bool

from kivy.properties import BooleanProperty
from kivy.uix.button import Button
from kivy.app import App

class MyApp(App):
    my_bool = BooleanProperty(False)

    def build(self):
        button = Button(text='Toggle Bool', on_release=self.toggle_bool)
        return button

    def toggle_bool(self, instance):
        self.my_bool = not self.my_bool

if __name__ == '__main__':
    MyApp().run()

from kivy.app import App

def update_bool(instance):
    app = App.get_running_app()
    app.my_bool = not app.my_bool

if __name__ == '__main__':
    update_bool(None)