如何在python canvas (KIVY)中引用widget的位置和大小？

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

class MyWidget(BoxLayout):
    def __init__(self, **kwargs):
        super(MyWidget, self).__init__(**kwargs)
        
        # 创建一个按钮
        button = Button(text='Hello World')
        self.add_widget(button)
        
        # 引用按钮的位置和大小
        print('Button position:', button.pos)
        print('Button size:', button.size)
        print('Button width:', button.width)
        print('Button height:', button.height)

class MyApp(App):
    def build(self):
        return MyWidget()

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