Kivy: get parent inside widget which is added in python

Question

How do I get the reference to a parent inside a widget that is not added by kvlang but in python. Normally you would just call self.parent however that returns Null if the widget is added in python to the parent.

An example:

import kivy
kivy.require('1.9.0') # replace with your current kivy version !

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager,Screen
from kivy.clock import Clock

kvlang = '''
<ScreenManagement>:
    ScreenOne:

<ScreenOne>:
    name: 'First'


<ScreenTwo>:
    name: 'Second'

'''


class ScreenManagement(ScreenManager):
    def __init__(self,**kwargs):
        super().__init__(**kwargs)

        def setup(*args):
            self.add_widget(ScreenTwo())    #add ScreenTwo later in python

        Clock.schedule_once(setup)

class ScreenOne(Screen):
    def __init__(self,**kwargs):
        super().__init__()

        def setup(*args):
            print("Parent of ScreenOne: {}".format(self.parent))        #this is working
        Clock.schedule_once(setup)

class ScreenTwo(Screen):
    def __init__(self,**kwargs):
        super().__init__()

        def setup(*args):
            print("Parent of ScreenTwo: {}".format(self.parent))        #this is not working, self.parent will return None
        Clock.schedule_once(setup)



class MyApp(App):

    def build(self):
        Builder.load_string(kvlang)
        return ScreenManagement()


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

This will return:

Parent of ScreenOne: <__main__.ScreenManagement object at 0x7f98a3fddb40>
Parent of ScreenTwo: None

Answer 1

Widgets added with add_widget actually has a valid reference to their parent:

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

from kivy.lang import Builder
Builder.load_string('''
<ScreenTwo>
    Label:
        text: 'Hello, world'    
''')

class ScreenManagement(ScreenManager):
    def __init__(self,**kwargs):
        super(ScreenManagement, self).__init__(**kwargs)
        screen = ScreenTwo()

        print(screen.parent)
        self.add_widget(screen)  
        print(screen.parent)


class ScreenTwo(Screen):
    def on_touch_down(self, *args):
        print(self.parent)


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


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

It's just not available in their __init__ method.