Observer Pattern – Behavioral – Python

The observer(subject) is an object that maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods.

Example – Python:

class Observable:
    def __init__(self):
        self.__observers = []
    
    def register_observer(self, observer):
        self.__observers.append(observer)
    
    def notify_observers(self, *args, **kwargs):
        for observer in self.__observers:
            observer.notify(self, *args, **kwargs)

class Observer:
    def __init__(self, observable):
        observable.register_observer(self)
    
    def notify(self, observable, *args, **kwargs):
        print('Got', args, kwargs, 'From', observable)


subject = Observable()
observer = Observer(subject)
subject.notify_observers('test')

output would be same as below  (except instance at will differ in memory address):

('Got', ('test',), {}, 'From', <__main__.Observable instance at 0x7efcf8d4e4d0>)