Running function from parent module which has a loop in it.

[Gribouillis]

What is the best way for two modules to work but with one slave child module to have the ability to run functions in the master function?

I think a simple way is to use classes and pass class instances as object parameters, for example

# parent.py
import uipart

class MusicPlayer:
    def play_music(self):
        ...

if __name__ == '__main__':
    player = MusicPlayer()
    ui = uipart.Ui(player)
    while True:
        ...

# uipart.py

class Ui:
    def __init__(self, player):
        self.player = player

    def spam(self):
        # call the parent's callback as a player instance's method
        self.player.play_music()

...