Understanding Python Decorators….It’s Just This Easy!

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Python decorators tended to confuse me far more than they needed to.
For instance:

@timer
def calculate_total():
    return sum(range(1_000_000))

And start wondering what really is happening.
What is this @timer doing? Does it alter the function somehow? Does it call the function itself? And why would I want to use this decorator and not just write the additional code myself within my function?
This looks complex, even intimidating, particularly when you meet decorators in frameworks like Flask, Django, and FastAPI for the first time.
But this is what finally put all things together for me:
A decorator is just a function that takes a function as an argument and returns a function, usually adding some functionality around the original one.
It’s this simple. Once you get it, understanding logging, performance measurement, authentication checks, and function decorators becomes easy.
Let us build this concept from scratch using regular Python functions.

1. First, Understand That Functions Are Objects