{"id":489,"date":"2020-10-13T02:37:57","date_gmt":"2020-10-13T02:37:57","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=489"},"modified":"2025-03-31T02:29:41","modified_gmt":"2025-03-31T02:29:41","slug":"python-keyword-arguments","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-basics\/python-keyword-arguments\/","title":{"rendered":"Python Keyword Arguments"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about the Python keyword arguments, and how to use them to make function calls more obvious.<\/p>\n\n\n\n

Introduction to the Python keyword arguments #<\/a><\/h2>\n\n\n\n

Let’s start with a simple function<\/a> that calculates the net price from the selling price and discount:<\/p>\n\n\n

def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The get_net_price()<\/code> function has two parameters: price<\/code> and discount<\/code>.<\/p>\n\n\n\n
The following shows how to call the get_net_price()<\/code> function to calculate the net price from the price 100<\/code> and discount 10%<\/code>:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(100<\/span>, 0.1<\/span>)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
 90.00<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In the get_net_price(100, 0.1)<\/code> function call, we pass each argument as a positional argument. In other words, we pass the price<\/code> argument first and the discount<\/code> argument second.<\/p>\n\n\n\n
However, the function call get_net_price(100, 0.1)<\/code> has a readability issue. Because by looking at that function call only, you don’t know which argument is price<\/code> and which one is the discount<\/code>.<\/p>\n\n\n\n
On top of that, when you call the get_net_price()<\/code> function, you need to know the position of each argument. <\/p>\n\n\n\n
If you don’t, the function will calculate the net_price<\/code> incorrectly. For example:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(0.1<\/span>, 100<\/span>)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
-9.9<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To improve the readability, Python introduces keyword arguments.<\/p>\n\n\n\n
The following shows the keyword argument syntax:<\/p>\n\n\n
fn(parameter1=value1,parameter2=value2)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
By using the keyword argument syntax, you don’t need to specify the arguments in the same order as defined in the function. <\/p>\n\n\n\n
Therefore, you can call a function by swapping the argument positions like this:<\/p>\n\n\n
fn(parameter2=value2,parameter1=value1)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following shows how to use the keyword argument syntax to call the get_net_price()<\/code> function:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(\n    price=100<\/span>, \n    discount=0.1<\/span>\n)\n\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Or:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(\n    discount=0.1<\/span>,\n    price=100<\/span>\n)\n\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Both of them returns the same result.<\/p>\n\n\n\n
It is possible to leave a trailing comma after the last argument:<\/p>\n\n\n
def get_net_price(price, discount):\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(\n    discount=0.1<\/span>,\n    price=100<\/span>,\n)\n\nprint<\/span>(f'{net_price: .2f}'<\/span>)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
When you use the keyword arguments, their names that matter, not their positions.<\/p>\n\n\n
def get_net_price(price, discount):\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(\n    price=100<\/span>, \n    discount=0.1<\/span>\n)\nprint<\/span>(net_price)<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you can call a function by mixing positional and keyword arguments. For example:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, discount)<\/span>:<\/span>\n    return<\/span> price * (1<\/span>-discount)\n\nnet_price = get_net_price(\n    100<\/span>, \n    discount=0.1<\/span>\n)\n\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Keyword arguments and default parameters #<\/a><\/h2>\n\n\n\n
Suppose that you have the following get_net_price()<\/code> function that calculates the net price from the selling price, tax, and discount.<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The following calls the get_net_price()<\/code> function and uses the default values for tax<\/code> and discount<\/code> parameters:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(100<\/span>)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
101.65<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Suppose that you want to use the default value for the tax<\/code> parameter but not discount<\/code>. The following function call doesn’t work correctly.<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(100<\/span>, 0.06<\/span>)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
100.70<\/span><\/code><\/span>Code language:<\/span> CSS<\/span> (<\/span>css<\/span>)<\/span><\/small><\/pre>\n\n\n
… because Python will assign 100<\/code> to price and 0.1<\/code> to tax, not discount.<\/p>\n\n\n\n
To fix this, you must use keyword arguments:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(\n    price=100<\/span>, \n    discount=0.06<\/span>\n)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
100.58<\/code><\/span>Code language:<\/span> Shell Session<\/span> (<\/span>shell<\/span>)<\/span><\/small><\/pre>\n\n\n
Or you can mix the positional and keyword arguments:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(\n    100<\/span>, \n    discount=0.06<\/span>\n)\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
100.58<\/code><\/span>Code language:<\/span> Shell Session<\/span> (<\/span>shell<\/span>)<\/span><\/small><\/pre>\n\n\n
Python keyword argument requirements #<\/a><\/h2>\n\n\n\n
Once you use a keyword argument, you need to use keyword arguments for the remaining parameters.<\/p>\n\n\n\n
The following will result in an error because it uses the positional argument after a keyword argument:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(\n    100<\/span>, \n    tax=0.08<\/span>, \n    0.06<\/span>\n)\n\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Error:<\/p>\n\n\n
SyntaxError: positional argument follows keyword argument<\/code><\/span>Code language:<\/span> Shell Session<\/span> (<\/span>shell<\/span>)<\/span><\/small><\/pre>\n\n\n
To fix this, you need to use the keyword argument for the third argument like this:<\/p>\n\n\n
def<\/span> get_net_price<\/span>(price, tax_rate=0.07<\/span>, discount=0.05<\/span>)<\/span>:<\/span>\n    discounted_price = price * (1<\/span> - discount)  \n    net_price = discounted_price * (1<\/span> + tax_rate)  \n    return<\/span> net_price\n\nnet_price = get_net_price(\n    100<\/span>, \n    tax_rate=0.08<\/span>, \n    discount=0.06<\/span>\n)\n\nprint(f'{net_price: .2<\/span>f}<\/span>'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
101.52<\/code><\/span>Code language:<\/span> plaintext<\/span> (<\/span>plaintext<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
In the get_net_price()<\/code> function, the tax and discount parameters have default values<\/a> of 7%<\/code> and 5%<\/code> respectively.<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n
In this example, we use an f-string<\/a> to format the output number with two decimal places (f'{net_price: .2f}'<\/code>).<\/p>\n\n\n\n
Try it<\/a><\/p>\n\n\n\n