Decorate class

Learn to wrap all methods with a class decorator.

What is a class decorator?

A class decorator is a function that takes a class, modifies it and returns it. When you write @add_greet Python first creates class User, then calls add_greet(User).

Inside the decorator you can add new methods or wrap existing ones. You add members with cls.new_method = func. Finally you return cls. This is clearer than a metaclass: the class is fully built before you change it.

Wrapping all methods

A class decorator can iterate every method in a class and wrap it. You get the namespace dict with vars(cls) and select methods with callable(v).

You wrap each method in a wrapper function to add logging or timing. This pattern is more intuitive than a metaclass; the @decorator line makes the intent explicit. But wrapping every method needs care; you may want to skip dunder methods like __init__.

Exercise Write the greet decorator

Write a class decorator named add_greet taking cls. Inside it define a greet(self) method returning "merhaba". Attach it with cls.greet = greet and return cls. Write a User class tagged with @add_greet. Create an instance and print greet().

Show example solution

# Write the add_greet decorator
def add_greet(cls):
    def greet(self):
        return "merhaba"
    cls.greet = greet
    return cls

@add_greet
class User:
    pass

u = User()
print(u.greet())

Test yourself

Complete the decorator definition

def add_greet(____):
    cls.greet = lambda self: "merhaba"
    return cls

Show answer

def add_greet(cls):
    cls.greet = lambda self: "merhaba"
    return cls

What does a class decorator receive?
```
@add_greet
class User:
    pass
```
- The class name
- An instance
- The class object
- A list of methods
Show answer

The class object — A class decorator receives and returns the class object.
Match class decorator concepts

@decorator

Wraps the class
cls

The class object
vars(cls)

Namespace dict
wrapper

Wrapping function

Next lesson: Summary - Metaprogramming

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