What Are Decorators in Python?

Decorators were introduced in Python a long time ago, in PEP-318, as a mechanism to simplify the way functions and methods are defined when they have to be modified after their original definition.

We first have to understand that in Python, functions are regular objects just like pretty much anything else. That means we can assign them to variables, pass them around by parameters, or even apply other functions to them. It is typical to want to write a small function, and then apply some transformations to it, generating a new modified version of that function (similar to how function composition works in mathematics).

Motivation behind decorators

One of the original motivations for introducing decorators was that, because functions such as classmethod and staticmethod were used to transform the original definition of the method, they required an extra line, modifying the original definition of the function in a separate statement.

More generally speaking, every time we had to apply a transformation to a function, we had to call it with the modifier function, and then reassign it to the same name the function was originally defined with.

For instance, if we have a function called original, and then we have a function that changes the behavior of original on top of it, called modifier, we have to write something like this: