Python: Master the Art of Design Patterns

Chapter 5. The Decorator Pattern

Whenever we want to add extra functionality to an object, we have a number of different options. We can:

• Add the functionality directly to the class the object belongs to, if it makes sense (for example, add a new method)
• Use composition
• Use inheritance

Composition should generally be preferred over inheritance, because inheritance makes code reuse harder, it's static, and applies to an entire class and all instances of it [GOF95, page 31], [j.mp/decopat].

Design patterns offer us a fourth option that supports extending the functionality of an object dynamically (in runtime): Decorators. A Decorator pattern can add responsibilities to an object dynamically, and in a transparent manner (without affecting other objects) ...