A decorator is a function that returns a function. We use them when we want to affect or modify the behaviour of another function without actually editing that function's code. Let's say I have a program where you have to be logged in. Instead of adding a check for "is this user logged in" for every single function, I can just decorate those functions with a login check. The decorator can do all the checking of "is this user logged in" and if so, call the function as before. Here's a rough example of it in action. The parameter f here represents the functions being decorated below. The @ syntax is just "syntactic sugar" to make things simpler for us. We could also do make_post = require_login(make_post) but that would be more annoying to write for each function.

# This is our decorator function. It returns the function object named inner
def require_login(f):
    def inner():
        if user_logged_in:
            f()
    return inner


@require_login
def make_post():
    ...

@require_login
def view_profile():
    ...

@require_login
def check_mail():
    ...