Keyword-Only Arguments in Python

Understanding Keyword-Only Arguments in Functions

Defining keyword-only arguments in a function can significantly enhance readability and usability by prompting users to provide arguments with explicit names. This is particularly useful when a function has many parameters, which might lead to confusion if users mix their order. Let's dive into how you can achieve this in your functions.

What Are Keyword-Only Arguments?

Keyword-only arguments are those that must be specified using the keyword and cannot be provided as positional arguments. They improve code clarity. For example: def greet(name, , age): print(f"Hello, {name}. You are {age} years old.") In this case, `name` can be passed as a positional argument, while `age` must be presented as a keyword (e.g., `greet("Alice", age=30)`).

How to Define Keyword-Only Arguments

To implement keyword-only argument functionality in your Python functions, you can follow these steps:

Define the function.
Place an asterisk () in the parameter list where keyword-only arguments start.
Declare your keyword-only arguments after the asterisk.

Example Implementation

Here’s a clear example: def order_item(item_name, , quantity=1, size='M'): print(f"Ordering {quantity} of {item_name} in size {size}.") This function requires `item_name` to be a positional argument, while `quantity` and `size` are keyword-only arguments.

Benefits of Using Keyword-Only Arguments

- Clarity: Makes the function calls easier to read. - Flexibility: Allows for default values without requiring all parameters to be supplied in order. - Maintainability: Changes in the function parameters won’t affect existing calls as significantly.

Use Cases

Consider the following scenarios where keyword-only arguments can be particularly helpful:

Functions with multiple optional parameters.
Functions meant for API or library design, improving user experience.
When supporting legacy code that previously accepted positional arguments but needs refactoring.

Conclusion

Using keyword-only arguments can simplify your code significantly and enhance its clarity. They allow a more structured way to call functions, especially when there are optional parameters. Adopting this feature may require some initial adjustments in your coding style, but the readability and maintainability benefits are certainly worth it.

Update: 17 Jun 2026