I think Melan did a wonderful job at answering this 
just a small detail, I’d probably set “self.button” to “None” inside of the init of your Example class in this case (don’t forget to call super().init(self) !), so that you can simplify your test to “if self.kivy_app.button” instead of using “hasattr()”.
(Also FYI Melan, I saw your issues, just a bit busy at the moment )