Python *args and **kwargs

Posted in Python by Dirk - last update: Feb 14, 2024

What are *args

In Python, *args is a syntax that allows a function to accept a variable number of positional arguments. The asterisk (*) is used in the function definition to collect any additional positional arguments passed to the function into a tuple. The name args is a convention, you can use any valid variable name preceded by the asterisk.

*args example

def print_arguments(*args):
    for arg in args:
        print(arg)

# Using the function with different numbers of arguments
print_arguments(1, 2, 3)        # Output: 1 2 3
print_arguments("a", "b")       # Output: a b
print_arguments("x", 10, True)  # Output: x 10 True

In this example, the print_arguments function accepts any number of positional arguments, and the *args syntax collects them into the args tuple. The function then prints each argument.

As mentioned before, it’s important to note that the name args is a convention, and you could use any other valid variable name preceded by the asterisk. For example, you could use *values or *items instead of *args. The asterisk (*) indicates that the function can accept a variable number of arguments, and the actual variable name is up to the programmer’s preference.

What are **kwargs

In Python, **kwargs is a syntax that allows a function to accept a variable number of keyword arguments. Similar to *args, the double asterisk (**) is used in the function definition to collect any additional keyword arguments passed to the function into a dictionary. The name kwargs is a convention, but like *args, you can use any valid variable name preceded by the double asterisk.

**kwargs example:

def print_key_value_pairs(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

# Using the function with different keyword arguments
print_key_value_pairs(name="Alice", age=25, city="Wonderland")

In this example, the print_key_value_pairs function accepts any number of keyword arguments, and the **kwargs syntax collects them into the kwargs dictionary. The function then prints each key-value pair. output:

name: Alice
age: 25
city: Wonderland

It’s worth noting that you can use both *args and **kwargs in the same function definition if you want to create a function that accepts both positional and keyword arguments with variable lengths.

When to use *args and **kwargs

You use *args and **kwargs when you want to create functions that can accept a variable number of arguments, either positional or keyword arguments, respectively. These features provide flexibility in function definitions, allowing you to handle different scenarios where the number of arguments may vary.

Combined *args and **kwargs example

You can use both *args and **kwargs in the same function definition when you need to handle both positional and keyword arguments with variable lengths.

def process_data(*args, **kwargs):
    # Code to process positional arguments in args
    for arg in args:
        # process arg

    # Code to process keyword arguments in kwargs
    for key, value in kwargs.items():
        # process key-value pair