Python Decorators Explained

Decorators look intimidating at first, but the idea behind them is simple. A decorator is a function that adds behavior to another function without changing its code. Once the concept clicks, you will see decorators everywhere in Python.

Functions Are Objects

The key idea is that functions in Python are values. You can pass them around, store them in variables, and return them from other functions.

def greet():
    return "hello"

say = greet
print(say())

A Function That Wraps Another

A decorator takes a function, wraps it in extra logic, and returns the new version. Here a wrapper makes any greeting uppercase.

def shout(func):
    def wrapper():
        return func().upper()
    return wrapper

def greet():
    return "hello"

loud = shout(greet)
print(loud())

The @ Syntax

Python offers a shortcut. Placing the decorator name with an at sign above a function applies it automatically. The result is identical to the manual version above.

def shout(func):
    def wrapper():
        return func().upper()
    return wrapper

@shout
def greet():
    return "hello"

print(greet())

Handling Any Arguments

Real functions take arguments, so a flexible wrapper uses args and kwargs to pass everything through untouched.

def logged(func):
    def wrapper(*args, **kwargs):
        print("Calling", func.__name__)
        return func(*args, **kwargs)
    return wrapper

@logged
def add(a, b):
    return a + b

print(add(2, 3))

Decorators That Take Arguments

Sometimes you want to configure a decorator, such as repeating a call a set number of times. This needs one more layer of functions.

def repeat(n):
    def decorator(func):
        def wrapper():
            for _ in range(n):
                func()
        return wrapper
    return decorator

@repeat(3)
def hi():
    print("hi")

hi()

Where You Will See Them

Web frameworks use decorators to connect routes, testing tools use them to mark tests, and caching libraries use them to store results. Learning the pattern once unlocks all of these tools.

Try It Yourself

Open the playground and write a decorator that prints the word done after a function runs. Building one from scratch is the fastest way to truly understand decorators.