What is a class decorator and how is it different from a function decorator?

Question

Accepted Answer

**Class decorator** is a function that takes a **class** and returns a modified class.

```python
import functools

# Class decorator with function
def add_repr(cls):
    @functools.wraps(cls)
    def wrapper(*args, **kwargs):
        return cls(*args, **kwargs)

def __repr__(self):
        attrs = ", ".join(f"{k}={v!r}" for k, v in self.__dict__.items())
        return f"{cls.__name__}({attrs})"

wrapper.__repr__ = __repr__
    return wrapper

@add_repr
class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

p = Point(1, 2)
print(p)  # Point(x=1, y=2)

# Class decorator with class
debug_all(cls):
    for name, method in vars(cls).items():
        if callable(method):
            def debug_method(m):
                def wrapper(self, *args, **kwargs):
                    print(f"Calling {m.__name__}")
                    return m(self, *args, **kwargs)
                return wrapper
            setattr(cls, name, debug_method(method))
    return cls
```

**Use cases:**
- Adding methods/attributes.
- Registration pattern.
- Validation.

Python: What is a class decorator and how is it different from a function decorator?