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Mastering the Art of Programming in Python 3

Functions with Optional Arguments

Explore how to define Python functions that accept optional arguments using *args for positional and **kwargs for keyword arguments. Understand how these features enhance function flexibility and make your code more adaptable to different input scenarios.

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This section brings detailed information about an eminently used feature in Python programming. Getting a firm hold on this concept will make you a competent developer, as it brings wonders.

The *args and **kwargs parameters

The args and kwargs parameters allow a function to accept optional arguments.

  • The keyword args means positional arguments.
  • The keyword kwargs means keyword arguments.

Let’s see a simple example to get a basic understanding of these parameters.

Python 3.10.4
def func(fixed, *args, **kwargs):
    print(fixed)
    if args:    # Optional positional arguments
        print(args)
    if kwargs:  # Optional keyword arguments
        print(kwargs)
func('Educative')
func('Eduactive', 1, 2, 3)
func('Eduactive', 1, 2, 3, level='advanced', language='Python3')

In the code above, we define a function func at line 1. It takes one required argument: fixed. If func doesn’t get the required argument, it will generate an error. The next two parameters are optional arguments. The *args will collect all positional arguments in the form of a tuple. Whereas, **kwargs will collect all keyword arguments as a dictionary. Then we are printing all the arguments one by one. We are validating the existence of positional and keyword arguments with if structure (at line 3 and line 5 respectively). Now, we start calling func in different ways:

  • Look at line 8. We are calling func with one argument: Educative. Without any doubt, it will be assigned to fixed argument. The function func will only print Educative because args and kwargs are not present.
  • Look at line 10. We are calling func with four arguments: Educative, 1, 2, and 3. Here, Educative will be assigned to fixed argument. However, 1, 2, and 3 will be retrieved as a tuple by *args. The function func will print:
    • Educative
    • (1, 2, 3)
  • Look at line 12. We are calling func with six arguments: Educative, 1, 2, 3, level=‘advanced’, and language=‘Python3’. Here, Educative will be assigned to fixed argument. However, 1, 2, and 3 will be retrieved as a tuple by *args. Whereas, level=‘advanced’, and language=‘Python3’ will be retrieved as a dictionary by **kwargs. The function func will print:
    • Educative
    • (1, 2, 3)
    • {‘language’: ‘Python3’, ‘level’: ‘advanced’}

⚙️ Note: The actual syntax is * and **. Calling them args and kwargs is just a convention.