class Observer():
    _observers = []

    def __init__(self):
        self._observers.append(self)
        self._observed_events = []

    def observe(self, event_name, callback_fn):
        self._observed_events.append({'event_name': event_name, 'callback_fn': callback_fn})

    def forget(self, event_name):
        for dict_item in self._observed_events:
            for key, val in dict_item.items():
                if val == event_name:
                    self._observed_events.remove(dict_item)


class Event():
    def __init__(self, event_name, *callback_args):
        for observer in Observer._observers:
            for observable in observer._observed_events:
                if observable['event_name'] == event_name:
                    observable['callback_fn'](*callback_args)