event.py

class Event:
    def __init__(self):
        # Initialise a list of listeners
        self.__listeners = []

    # Define a getter for the 'on' property which returns the decorator.
    @property
    def on(self):
        # A decorator to run addListener on the input function.
        def wrapper(func):
            self.add_listener(func)
            return func

        return wrapper

    # Add and remove functions from the list of listeners.
    def add_listener(self, func):
        if func in self.__listeners:
            return
        self.__listeners.append(func)

    def remove_listener(self, func):
        if func not in self.__listeners:
            return
        self.__listeners.remove(func)

    # Trigger events.
    def trigger(self, *args, **kwargs):
        # Run all the functions that are saved.
        if args is None:
            args = []
        for func in self.__listeners:
            func(*args, **kwargs)