Applies a decorator to alter or extend the behavior or attributes of a class.

Signals that the class is being intentionally modified or enhanced via a decorator, indicating a design decision to alter class creation or behavior.

When you need to apply a decorator to a class, such as for registering the class, adding class methods, modifying attributes, or implementing patterns like singleton or registration.

Used in Python metaprogramming where class decorators are employed for tasks like registering plugins, adding properties, enforcing interfaces, or altering class creation.

@<decorator> class <ClassName>: pass

@decorator class ClassName: pass

<decorator>: the decorator function or class to apply; <ClassName>: the name of the class being decorated

• @dataclass
• @property
• @staticmethod
• @classmethod
• @lru_cache
• @singleton

• Different decorator names (e.g.
• @my_decorator
• @register)
• different class names
• adding class body content instead of pass
• using multiple decorators.

Forgetting to return the class from the decorator (if returning a new class), applying decorator without parentheses when it requires arguments, confusing class decorators with function decorators, assuming the decorator modifies instances rather than the class itself.

Similar: function decorators, method decorators, property decorators. Contrasting: inheritance, composition, metaclasses.

May be confused with Java annotations or C# attributes, which have similar syntax but different semantics; ensure the decorator returns a class or modifies it in place.

• function decorator
• method decorator
• property decorator
• class decorator
• decorator pattern

The decorator receives the class object and must return a class (either the same modified class or a new class); if it returns None, the class is replaced with None, causing errors.

Signals that the class is being intentionally modified or enhanced, indicating a metaprogramming intent and alerting readers to look for decorator-defined behavior.

Think of a decorator as a label that modifies a class, like @dataclass adds generated methods.

Using class decorators to modify class behavior (e.g., adding attributes, methods)