meet it

A wraps extra behaviour around any function.

A decorator is a function that takes a function, wraps it, and returns the wrapped version. The is a closure: it remembers the original, runs some extra code, calls the original and hands back its answer.

Writing @shout on the line above def greet is shorthand for greet = shout(greet). Every call to greet now goes through the wrapper. Give the wrapper *args, **kwargs so it works for any function.

Add @functools.wraps(func) to the wrapper so the decorated function keeps its own name.

import functools

def shout(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        result = func(*args, **kwargs)
        return result.upper() + "!"
    return wrapper

@shout
def greet(name, greeting="hello"):
    return f"{greeting}, {name}"

print(greet("sam"), greet("ana", greeting="hi"), greet.__name__)

Without functools.wraps, greet.__name__ would say wrapper, which makes error messages confusing.

guess first

Follow every print. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

def announce(func):
    def wrapper(*args):
        print("Starting", func.__name__)
        answer = func(*args)
        print("Finished", func.__name__)
        return answer
    return wrapper

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

print(add(2, 3))

your turn

Your turn. Guard a function against empty text.

Put the decorator on shout in the first blank, with its @. In the second, type any word you like.

Your code

press run to see what happens

fix it

The decorator breaks the function. Fix it!

Broken code to fix

press run to see what happens

The error says NoneType is not callable. What did logged hand back to replace area?
logged builds a wrapper but never returns it, so it hands back None.
Add return wrapper at the end of logged, lined up with def wrapper, then run.

nailed it

you can wrap any function in new powers. :D

A decorator takes a function and returns a wrapped one.
@name above def means func = name(func).
Use *args, **kwargs and functools.wraps in every wrapper.

new words in your collection

decorator
wrapper

This lesson isn’t saved. A free account remembers every lesson you finish.

A decorator wraps extra behaviour around any function.

Follow every print. What will this show?

Your turn. Guard a function against empty text.

The decorator breaks the function. Fix it!

you can wrap any function in new powers. :D

A wraps extra behaviour around any function.