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Python Decorators

Learn what a Python decorator is and how to use it.

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Introduction to Python decorator

A Python decorator is a function that takes a function and replaces it with the modified version. Let’s look at an example.

Python 3.5
import time
def with_timer(f):
    def new_function(*args, **kwargs):
        start_time = time.time()
        result = f(*args, **kwargs)
        end_time = time.time()
        print('Elapsed time:', end_time - start_time)
        return result
    return new_function
@with_timer
def pointless_waiting(s):
    time.sleep(s)
    return 'Done'
pointless_waiting(2)

Explaining the code

The example defines a function called with_timer that takes in a function, f, and outputs a function new_function. The input function argument, f, is used inside new_function, but is sandwiched between timer computations and a timer output. The *args and **kwargs arguments are how we specify all positional and keyword arguments. The use of the function with_timer with the at-notation @ makes it a ...