如何在Kivy中使用创建圆形或圆形按钮。Kv，而不使用。Kv文件

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.floatlayout import FloatLayout
from kivy.graphics import Ellipse, Color

class CircleButton(Button):
    def __init__(self, **kwargs):
        super(CircleButton, self).__init__(**kwargs)
        self.size_hint = (None, None)
        self.width = 100
        self.height = 100

    def on_size(self, *args):
        self.canvas.before.clear()
        with self.canvas.before:
            Color(0.5, 0.5, 1)
            Ellipse(pos=self.pos, size=self.size)

class MyLayout(FloatLayout):
    def __init__(self, **kwargs):
        super(MyLayout, self).__init__(**kwargs)
        circle_button = CircleButton(text='Click me')
        circle_button.pos_hint = {'center_x': 0.5, 'center_y': 0.5}
        self.add_widget(circle_button)

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

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