change-function-behavior-with-decorators.md

Extend behavior of Python functions with decorators

To extend the behavior of a Python function without changing its implementation, you can decorate it.

The pattern looks like this:

def some_decorator(func):
    def wrapper():
        print("Run before the function")
        func()
    return wrapper

def say_hello():
    print("Hello")

say_hello = some_decorator(say_hello)

say_hello()
# Will print:
# Run before the function 
# Hello

Python provides syntactic sugar with the @ syntax:

def some_decorator(func):
    def wrapper():
        print("Run before the function")
        func()
    return wrapper

@some_decorator
def say_hello():
    print("Hello")

say_hello()
# Will print:
# Run before the function 
# Hello

The decorator pattern takes advantage of functions being first-class citizens in Python. This pattern is useful to modify function behavior without changing existing implementation. It's also a useful method for checking cached values, authentication tokens in web requests, etc. Read more on Code Ship and Real Python