Ошибка TypeErrot: object.__init__() takes no parameters. Как фиксить?

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

class MyApp(App):
	def build(self):
		return Button(text = "Кнопка", 
			front_size = 30, 
			on_press = self.callback)

	def callback(self, instance):
		print("Кнопка нажата.")

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