Writing a decorator in Python

Wrapping a function to add behavior around it.

import functools


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


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


loud = greet("world")

How it works

1. shout returns a wrapper that calls the original.
2. @functools.wraps keeps the wrapped name and docstring.
3. @shout above greet rebinds it to the wrapper.

Keywords and builtins used here

• def
• greet
• return
• shout
• wrapper

The run, in numbers

Lines

17

Characters to type

229

Tokens

71

Three-star pace

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At the three-star pace of 100 tokens a minute, this run takes about 43 seconds.

Type this snippet

Step 2 of 5 in Decorators & closures, step 6 of 53 in Pythonic Python.

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