Observer pattern

observer.py

class Subscriber:
    def __init__(self):
        self._observers = []

    def subscribe(self, observer):
        if not observer in self._observers:
            self._observers.append(observer)

    def unsubscribe(self, observer):
        try:
            self._observers.remove(observer)
        except ValueError:
            pass

    def notify(self):
        observer.notify() for observer in self._observers
	
class User(Subscriber):
    def save(self, data):
        self.data = data
        self.notify()