如何在没有kv文件的情况下打开新的kivy屏幕？

from kivy.app import App
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.uix.button import Button


class MainScreen(Screen):
    def __init__(self, **kwargs):
        super(MainScreen, self).__init__(**kwargs)
        self.add_widget(Button(text="Open New Screen", on_release=self.open_new_screen))

    def open_new_screen(self, instance):
        screen_manager = App.get_running_app().root
        new_screen = NewScreen(name="new_screen")
        screen_manager.add_widget(new_screen)
        screen_manager.current = "new_screen"


class NewScreen(Screen):
    def __init__(self, **kwargs):
        super(NewScreen, self).__init__(**kwargs)
        self.add_widget(Button(text="Go Back", on_release=self.go_back))

    def go_back(self, instance):
        screen_manager = App.get_running_app().root
        screen_manager.current = "main_screen"
        screen_manager.remove_widget(self)


class MyApp(App):
    def build(self):
        screen_manager = ScreenManager()
        screen_manager.add_widget(MainScreen(name="main_screen"))
        return screen_manager


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