What Is **kwargs

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 10, 2026

Quick Answer: **kwargs in Python allows functions to accept an arbitrary number of keyword arguments as a dictionary, collecting them by name at runtime. Introduced in Python 2.0 (October 2000), the double asterisk (**) prefix distinguishes it from *args, enabling flexible function signatures that handle variable named parameters without pre-definition. It's a convention-based syntax—kwargs stands for 'keyword arguments'—used in 85% of Python web development frameworks including Django and Flask.

Key Facts

**kwargs was introduced in Python 2.0 (released October 2000) as a core function parameter feature
The syntax creates a dictionary at runtime; individual kwargs parameters cannot have default values, but you can check dictionary keys to provide defaults
**kwargs must come last in parameter order after positional parameters and *args, following the sequence: (regular_params, *args, **kwargs)
Approximately 85% of Python web frameworks like Django and Flask use **kwargs for flexible configuration and initialization handling
You can unpack dictionaries into function calls using the same ** operator syntax, enabling bidirectional dictionary-to-kwargs transformation

Overview

**kwargs is a Python feature that allows functions to accept an arbitrary number of keyword arguments and collect them into a dictionary automatically. The double asterisks (**) prefix signals to Python that the following parameter should gather all keyword arguments passed at function call time into a single dictionary object. This mechanism enables developers to write flexible functions that can handle variable numbers of named parameters without explicitly defining each one in advance.

The term "kwargs" is short for "keyword arguments" and represents a naming convention that Python developers widely adopted since Python 2.0's release in October 2000. While you could technically use alternative names like **options or **params, **kwargs has become the standardized term in Python communities worldwide. It pairs naturally with *args, which handles positional arguments, creating a powerful combination for building functions that accept unlimited parameters of both types simultaneously.

How It Works

Understanding **kwargs requires seeing how Python processes function calls:

Dictionary Creation: When a function with **kwargs is invoked, Python automatically constructs a dictionary containing all keyword arguments provided by the caller. Parameter names become dictionary keys, and the supplied values become the corresponding dictionary values at call time.
Function Definition: To utilize **kwargs, you define a parameter with the ** prefix, such as def my_function(**kwargs). This syntax explicitly tells Python to expect and collect zero or more keyword arguments into a dictionary.
Accessing Arguments Inside Functions: Within the function body, you access collected arguments using dictionary syntax: kwargs['parameter_name'] for individual values or kwargs.items() to iterate through all key-value pairs simultaneously.
Combining with Other Parameter Types: Functions can combine **kwargs with regular positional parameters and *args, but they must follow a strict order: first positional parameters, then *args, then **kwargs at the end.
Handling Missing Keys: Since **kwargs captures only the keyword arguments explicitly passed, you must check if keys exist using 'key' in kwargs or use kwargs.get('key', default_value) to safely provide default values for optional parameters.

Key Comparisons

Python offers several mechanisms for handling variable parameters; understanding their differences is crucial:

Feature	Syntax	Data Structure	Primary Use Case
**kwargs	def func(**kwargs)	Dictionary with string keys	Variable named parameters, flexible APIs, configuration passing
*args	def func(*args)	Tuple of positional values	Variable positional parameters, variable-length argument lists
Regular Parameters	def func(a, b, c)	Specific named variables	Required parameters with known names and count
Default Parameters	def func(a=10, b=20)	Named variables with fallback values	Optional parameters with predefined defaults

Why It Matters

API Flexibility and Evolution: **kwargs enables building functions that gracefully accept unknown or additional parameters without requiring pre-definition, crucial for decorator patterns, wrapper functions, and plugin systems that must accommodate future requirements and new parameters added in later versions.
Framework Standard Adoption: Major Python web frameworks like Django (request handlers) and Flask (route decorators) extensively rely on **kwargs for flexible configuration and initialization, with approximately 85% of Python web development libraries implementing this pattern as standard practice.
Backward Compatibility: When building libraries or APIs, **kwargs allows accepting optional configuration parameters without breaking existing code when new features are added in future releases, maintaining seamless backward compatibility across versions.
Dictionary Unpacking Symmetry: **kwargs works bidirectionally in Python—you can collect keyword arguments into functions and also unpack dictionaries into function calls using the ** operator, enabling seamless transformation between dictionary data structures and keyword arguments.

Mastering **kwargs represents a fundamental skill for writing production-grade Python code that remains flexible and maintainable as requirements evolve. It's particularly essential when implementing decorators, building configuration systems, or developing reusable components that must handle variable inputs gracefully. The ability to distinguish between when to use **kwargs, *args, and regular parameters separates beginner-level Python implementations from professional code that scales across complex systems and adapts to changing needs without requiring complete rewrites.