Python **kwargs

Summary: in this tutorial, you’ll learn about the Python **kwargs parameters.

Introduction to the Python **kwargs parameters

In Python, a function can have a parameter preceded by two stars (**). For example: **kwwargs

The **kwargs is called a keyword parameter.

When a function has the **kwargs parameter, it can accept a variable number of keyword arguments as a dictionary.

The two stars (**) are important. However, the name kwargs is by convention. Therefore, you can use any other meaningful names such as **configs and **files.

The following example defines a function called connect() that accepts a **kwargs parameter:

def connect(**kwargs):
    print(type(kwargs))
    print(kwargs)Code language: Python (python)

The following function call shows an empty dictionary to the screen:

connect()Code language: Python (python)

Output:

<class 'dict'>
{}Code language: Python (python)

In this example, we didn’t pass any arguments to the connect() function, the kwargs is empty dictionary.

The following calls the connect() function and passes some keyword arguments into it:

connect(server='localhost', port=3306, user='root', password='Py1hon!Xt')Code language: Python (python)

It shows the following dictionary to the screen:

<class 'dict'>
{'server': 'localhost', 'port': 3306, 'user': 'root', 'password': 'Py1hon!Xt'}Code language: Python (python)

Inside the connect() function, you can use the kwargs argument as a dictionary.

If you want to pass a dictionary to the function, you need to add two stars (**) to the argument like this:

def connect(**kwargs):
    print(kwargs)


config = {'server': 'localhost',
        'port': 3306,
        'user': 'root',
        'password': 'Py1thon!Xt12'}

connect(**config)Code language: Python (python)

If a function has the **kwargs parameter and other parameters, you need to place the **kwargs after other parameters. Otherwise, you’ll get an error.

The syntax of the following connect() function is correct:

def connect(fn, **kwargs):
    print(kwargs)Code language: Python (python)

However, the syntax of this function causes a SyntaxError:

def connect(**kwargs, fn):
    print(kwargs)Code language: Python (python)

Using both *args and **kwargs arguments

The following function has both *args and **kwargs parameters:

def fn(*args, **kwargs):
    print(args)
    print(kwargs)Code language: PHP (php)

The fn function can accept a variable number of the positional arguments. Python will pack them as a tuple and assign the tuple to the args argument.

The fn function also accepts a variable number of keyword arguments. Python will pack them as a dictionary and assign the dictionary to the kwargs argument.

For example:

fn(1, 2, x=10, y=20)

Output:

(1, 2)
{'x': 10, 'y': 20}Code language: JavaScript (javascript)

Summary

• Use the Python **kwargs parameter to allow the function to accept a variable number of keyword arguments.
• Inside the function, the kwargs argument is a dictionary that contains all keyword arguments as its name-value pairs.
• Precede double stars (**) to a dictionary argument to pass it to **kwargs parameter.
• Always place the **kwargs parameter at the end of the parameter list, or you’ll get an error.