{"id":977,"date":"2020-11-06T09:47:02","date_gmt":"2020-11-06T09:47:02","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=977"},"modified":"2025-03-27T13:50:42","modified_gmt":"2025-03-27T13:50:42","slug":"python-decorators","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/advanced-python\/python-decorators\/","title":{"rendered":"Python Decorators"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python decorators and how to develop your own decorators.<\/p>\n\n\n\n

What is a decorator in Python #<\/a><\/h2>\n\n\n\n

A decorator is a function<\/a> that takes another function as an argument and extends its behavior without changing the original function explicitly.<\/p>\n\n\n\n

Let’s take a simple example to understand the concept.<\/p>\n\n\n\n

A simple Python decorator example #<\/a><\/h2>\n\n\n\n

The following defines a net_price<\/code> function:<\/p>\n\n\n

def<\/span> net_price<\/span>(price, tax)<\/span>:<\/span>\n    \"\"\" calculate the net price from price and tax\n    Arguments:\n        price: the selling price\n        tax: value added tax or sale tax\n    Return\n        the net price\n    \"\"\"<\/span>\n    return<\/span> price * (1<\/span> + tax)\n<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The net_price<\/code> function calculates the net price from selling price and tax. It returns the net_price<\/code> as a number.<\/p>\n\n\n\n
Suppose that you need to format the net price using the USD currency. For example, 100<\/code> becomes $100<\/code>. To do it, you can use a decorator.<\/p>\n\n\n\n
By definition, a decorator is a function that takes a function as an argument:<\/p>\n\n\n
def<\/span> currency<\/span>(fn)<\/span>:<\/span>\n    pass<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
And it returns another function:<\/p>\n\n\n
def<\/span> currency<\/span>(fn)<\/span>:<\/span>\n    def<\/span> wrapper<\/span>(*args, **kwargs)<\/span>:<\/span>\n        fn(*args, **kwargs)\n\n    return<\/span> wrapper<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The currency<\/code> function returns the wrapper<\/code> function. The wrapper<\/code> function has the *args<\/code> and **kwargs<\/code> parameters.<\/p>\n\n\n\n
In this example, the wrapper<\/code> function essentially executes the fn<\/code> function directly and doesn’t change any behavior of the fn<\/code> function.<\/p>\n\n\n\n
In the wrapper<\/code> function, you can call the fn<\/code> function, get its result, and format the result as a currency string:<\/p>\n\n\n
def<\/span> currency<\/span>(fn)<\/span>:<\/span>\n    def<\/span> wrapper<\/span>(*args, **kwargs)<\/span>:<\/span>\n        result = fn(*args, **kwargs)\n        return<\/span> f'${result}<\/span>'<\/span>\n    return<\/span> wrapper<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The currency<\/code> function is a decorator. <\/p>\n\n\n\n
It accepts any function that returns a number and formats that number as a currency string.<\/p>\n\n\n\n
To use the currency<\/code> decorator, you need to pass the net_price<\/code> function to it to get a new function and execute the new function as if it were the original function. For example:<\/p>\n\n\n
def<\/span> currency<\/span>(fn)<\/span>:<\/span>\n    def<\/span> wrapper<\/span>(*args, **kwargs)<\/span>:<\/span>\n        result = fn(*args, **kwargs)\n        return<\/span> f'${result}<\/span>'<\/span>\n    return<\/span> wrapper\n\nnet_price = currency(net_price)\nprint(net_price(100<\/span>, 0.05<\/span>))<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
$105.0<\/code><\/span><\/pre>\n\n\n
Python decorator definition #<\/a><\/h2>\n\n\n\n
In general, a decorator is:<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
These parameters allow you to call any fn<\/code> function with any combination of positional and keyword-only arguments<\/a>.<\/p>\n\n\n\n