Understanding Decorators

A decorator is a design pattern in Python that allows a user to add new functionality to an existing object without modifying its structure.

Decorators are usually called before the definition of a function you want to decorate.

Basic Example

Here is how you define a simple decorator:

def my_decorator(func):
    def wrapper():
        print("Something is happening before the function is called.")
        func()
        print("Something is happening after the function is called.")
    return wrapper

@my_decorator
def say_whee():
    print("Whee!")

say_whee()

Explanation

The @my_decorator syntax is just syntactic sugar.
It passes the say_whee function to my_decorator.
It replaces say_whee with the returned wrapper function.

You will see decorators everywhere in frameworks like Flask or FastAPI!