如何访问嵌套按钮的on_press处理程序？

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

class MyButtonApp(App):
    def build(self):
        outer_button = Button(text='Outer Button')
        inner_button = Button(text='Inner Button')

        def inner_button_on_press(instance):
            print('Inner Button Pressed')

        def outer_button_on_press(instance):
            print('Outer Button Pressed')
            inner_button_on_press(inner_button)

        outer_button.bind(on_press=outer_button_on_press)

        return outer_button

MyButtonApp().run()