Observer

Observer is an abstract base class used for implementing the Observer design pattern in Python. subclasses of the Observer class should implement the update method, which is called whenever a subject the observer is watching changes.

Overview

The Observer class provides a template for creating objects that watch or monitor other objects (subjects). If a subject changes, it calls the update method in its observers.

Example

The following is an example demonstrating how to implement an instance of Observer class by implementing the update method.

class CustomObserver(Observer):
    def update(self, subject: Any):
        print(f"Subject {subject} has changed.")

Limitations

The Observer class is an abstract base class, so it cannot be instantiated on its own. Instead, you need to create a subclass and implement the update method.

Follow-up Questions:

What are the specification and role of the subject parameter in the update method?
What exact changes in the subject cause the update method to be called?