Advanced OOP

Class Decorators

Decorators that modify or enhance classes

Interview: Advanced patterns — tests understanding of decorator mechanics and class transformation

Last Updated: June 12, 2026 • 6 min read

Class decorators are functions that take a class and return a modified class. They provide a cleaner alternative to metaclasses for many use cases. Common patterns include adding methods, wrapping methods, enforcing singletons, and registering classes. The @dataclass decorator is the most famous example.

How Class Decorators Work

A function that takes a class as argument and returns a class
Applied with @decorator syntax above the class definition
Can modify the class in-place or return a new class
Simpler and more explicit than metaclasses for most use cases

Class Decorators vs Metaclasses

Decorators: Explicit, simple, don't affect inheritance

Metaclasses: Affect all subclasses, more powerful but complex

Prefer decorators when you don't need inheritance propagation

Interview Tip

Know the key difference: class decorators only affect the decorated class; metaclasses affect the class AND all its subclasses. Choose based on whether you need propagation.

Use Cases

Singleton pattern without metaclass complexity

Auto-generating __repr__, __eq__, __hash__ (like @dataclass)

Logging/wrapping all public methods in a class

Plugin/handler registration systems

Adding validation, caching, or timing to class methods

Common Mistakes

Class decorators don't propagate to subclasses (use metaclasses for that)

Forgetting to return the class from the decorator function

Modifying class in-place vs replacing it (affects isinstance checks)

Losing the original class name/docstring when wrapping

Using class decorators when @dataclass or other stdlib options exist