A decorator is a function that takes another function as a input, and does something with it. Say we have two functions:

def FunctionA():
    print('something')

def FunctionB(someFunction):
    someFunction()

FunctionB(FunctionA)

Function B is a decorator. Running this would return:

something

Decorators can be used for many things like monitoring the output of functions or calling a function multiple times

Pie Syntax

Decorator functions are usually called using Pie syntax. It looks like this:

def FunctionA():
    print('something')

@FunctionB
def FunctionA():
    print('something')

This is the python way of doing:

FunctionA(FunctionB())

Real Example

Flask

Flask is a Python application framework. Decorators are used in Flask web controllers to map URLs to the functions they perform. For example:

@app.route('/home')
def home()
    return('You are home')

If a user went to the URL /home the decorator app.route() would execute the function returning “You are home”.