How do I implement the Observer pattern in Python?

How do I implement the Observer pattern in Python?

The Observer pattern is a behavioral design pattern that allows an object, known as the subject, to maintain a list of its dependents, called observers, and notify them of state changes. Would you like a code example?

Yes, please provide a code example.

Here's a simple implementation:

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

    def attach(self, observer):
        self._observers.append(observer)

    def detach(self, observer):
        self._observers.remove(observer)

    def notify(self):
        for observer in self._observers:
            observer.update()

class Observer:
    def update(self):
        print("Observer has been notified!")

# Usage
subject = Subject()
observer1 = Observer()
subject.attach(observer1)
subject.notify()  # Output: Observer has been notified!

This code defines a Subject class that can attach and notify observers.

What if I want to pass data to the observers?

You can modify the notify method to accept data and pass it to the observers. Here's an updated example:

class Observer:
    def update(self, data):
        print(f"Observer received data: {data}")

class Subject:
    # ... (rest of the class remains the same)
    def notify(self, data):
        for observer in self._observers:
            observer.update(data)

# Usage
subject = Subject()
observer1 = Observer()
subject.attach(observer1)
subject.notify('Hello, Observers!')  # Output: Observer received data: Hello, Observers!

Thanks! This is really helpful.