observer.py

# ------------------------------
# Observer Design Pattern
# ------------------------------
# Define a one-to-many dependency between objects
# where a state change in one object results in all its dependents being notified and updated automatically.


class Subject:
    def __init__(self):
        self.__observers = []

    def register(self, observer):
        self.__observers.append(observer)

    def notify(self, *args, **kwargs):
        for observer in self.__observers:
            observer.notify(self, *args, **kwargs)


class Observer1:
    def __init__(self, subject):
        subject.register(self)

    def notify(self, subject, *args):
        print(type(self).__name__,': Got', args, 'From', subject)


class Observer2:
    def __init__(self, subject):
        subject.register(self)

    def notify(self, subject, *args):
        print(type(self).__name__, ': Got', args, 'From', subject)


subject = Subject()

# ----------------------------
# Registers observer with subject
#--------------------------------
observer1 = Observer1(subject)
observer2 = Observer2(subject)

subject.notify('Notification.')