In Python, a decorator is a design pattern that we can use to add new functionality to an already existing object without the need to modify its structure. A decorator should be called directly before the function that is to be extended. With decorators, you can modify the functionality of a method, a function, or a class dynamically without directly using subclasses. This is a good idea when you want to extend the functionality of a function that you don't want to directly modify. Decorator patterns can be implemented everywhere, but Python provides more expressive syntax and features for that.