如何在Kivy中通过按钮更改变量的值

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

class MyApp(App):
    def __init__(self, **kwargs):
        super(MyApp, self).__init__(**kwargs)
        self.my_variable = "Initial Value"

    def change_variable(self, instance):
        self.my_variable = "New Value"

    def build(self):
        layout = BoxLayout(orientation='vertical')
        label = Label(text=self.my_variable)
        button = Button(text='Change Variable')
        button.bind(on_press=self.change_variable)
        layout.add_widget(label)
        layout.add_widget(button)
        return layout

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