kivy python passing parameters to fuction with button click

Question

I am having trouble passing parameters to function when calling it with button press. One could do it like this in kivy language:

Button: 
   on_press: root.         


        

Answer 1

Button(on_press=self.my_function)

This is passing the function as an argument.

Button(on_press=self.my_function('btn1'))

This is calling the function and passing the returned value as the argument to on_press. Since the returned value is None, you get your error.

You instead need to pass a new function that calls your normal function and automatically passes the argument. In general, it's convenient to use functools.partial:

from functools import partial
Button(on_press=partial(self.my_function, 'btn1'))

You can also use a lambda function:

Button(on_press=lambda *args: self.my_function('btn1', *args))