当我在我的安卓槽构建器上构建Kivy应用程序时，我收到了ReferenceError

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

class MyApp(App):
    def build(self):
        btn = Button(text="Click Me")
        btn.bind(on_press=self.on_button_press)
        return btn

    def on_button_press(self, instance):
        print(undefined_var)  # 这里会引发ReferenceError

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

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

class MyApp(App):
    def build(self):
        btn = Button(text="Click Me")
        btn.bind(on_press=self.on_button_press)
        return btn

    def on_button_press(self, instance):
        defined_var = "Button Pressed!"  # 定义变量
        print(defined_var)  # 正确引用变量

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