如何在kivy中更改另一个屏幕上按钮的文本(没有kv lang)

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button

class MyScreenManager(ScreenManager):
    pass

class Screen1(Screen):
    pass

class Screen2(Screen):
    pass

class Screen1(Screen):
    def change_button_text(self):
        screen2 = self.manager.get_screen('screen2')
        button = screen2.ids.my_button
        button.text = 'New Text'

class Screen2(Screen):
    pass
    def __init__(self, **kwargs):
        super(Screen2, self).__init__(**kwargs)
        self.ids.my_button = Button(text='Old Text')
        self.add_widget(self.ids.my_button)

class MyApp(App):
    def build(self):
        screen_manager = MyScreenManager()
        screen_manager.add_widget(Screen1(name='screen1'))
        screen_manager.add_widget(Screen2(name='screen2'))
        return screen_manager

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