intermediate

Keyword Arguments (**kwargs)

Learn to accept any number of keyword arguments with **kwargs.

**kwargs allows functions to accept any number of keyword arguments, providing ultimate flexibility for function calls with named parameters stored as a dictionary.

📚 Concepts & Theory

kwargs allows functions to accept any number of keyword (named) arguments. The double asterisk () unpacks keyword arguments into a dictionary.

Basic kwargs Syntax:

def function_name(kwargs):

    # kwargs is a dictionary

    for key, value in kwargs.items():

        print(f"{key}: {value}")

Simple Example:

def print_info(kwargs):

    for key, value in kwargs.items():

        print(f"{key} = {value}")

print_info(name="Alice", age=30, city="NYC")

# name = Alice

# age = 30

# city = NYC

Building User Profiles:

def create_profile(details):

    profile = {

        "username": details.get("username", "anonymous"),

        "email": details.get("email"),

        "age": details.get("age"),

    }

    return profile

user = create_profile(username="alice", email="[email protected]", age=25)

Accessing kwargs:

def process(kwargs):

    # Get with default

    name = kwargs.get("name", "Unknown")

    

    # Check if key exists

    if "age" in kwargs:

        print(f"Age: {kwargs['age']}")

    

    # Iterate all

    for key, value in kwargs.items():

        print(f"{key}: {value}")

Mixing Parameters with kwargs:

def greet(greeting, kwargs):

    name = kwargs.get("name", "there")

    age = kwargs.get("age")

    

    msg = f"{greeting}, {name}!"

    if age:

        msg += f" You are {age} years old."

    return msg

greet("Hello", name="Alice", age=30)

Complete Parameter Order:**

def full_function(required, *args, keyword_only, **kwargs):

    pass

# Call examples:

full_function(

    1,                    # required

    2, 3,                 # *args

    keyword_only=4,       # keyword_only

    extra1=5,             # kwargs

    extra2=6              # kwargs

)

Common Use Cases:

1. Configuration Functions:

def configure_server(config):

    host = config.get("host", "localhost")

    port = config.get("port", 8080)

    debug = config.get("debug", False)

    return f"Server: {host}:{port} (debug={debug})"

configure_server(host="0.0.0.0", port=5000, debug=True)

2. Building Dictionaries:

def build_user(data):

    return {

        "id": data.get("id"),

        "name": data.get("name", "Anonymous"),

        "created": datetime.now(),

        data  # Include all other kwargs

    }

3. Flexible Object Creation:

def create_car(specs):

    car = {

        "brand": specs.get("brand", "Unknown"),

        "model": specs.get("model", "Unknown"),

        "year": specs.get("year", 2024)

    }

    car.update(specs)  # Add any additional specs

    return car

Unpacking Dictionaries:

def greet(name, age):

    return f"{name} is {age}"

user_data = {"name": "Alice", "age": 30}

result = greet(user_data)  # Unpacks dict into kwargs

# Same as: greet(name="Alice", age=30)

Combining *args and kwargs:

def super_flexible(*args, kwargs):

    print("Positional:", args)

    print("Keyword:", kwargs)

super_flexible(1, 2, 3, name="Alice", age=30)

# Positional: (1, 2, 3)

# Keyword: {'name': 'Alice', 'age': 30}

Forwarding Arguments:

def wrapper(kwargs):

    # Pass all kwargs to another function

    return actual_function(kwargs)

Type Hints (Python 3.8+):

from typing import Any

def process(kwargs: Any) -> dict:

    return kwargs

Best Practices:

Use descriptive parameter name: options, settings, **metadata

Document expected keywords

Provide sensible defaults with .get()

Validate required keywords

Consider if explicit parameters would be clearer

🎯 Your Challenge

Create a function build_user(**user_data) that creates and returns a dictionary with all provided keyword arguments.

📝 Starter Code

Python

def build_user(**user_data):
    pass

Use **user_data to accept any keyword arguments
**kwargs automatically creates a dictionary
Simply return the user_data dictionary
No need for loops or processing in this simple case
The function should accept and return all provided keyword arguments

Solution

Python

def build_user(**user_data):
    return user_data

Explanation

This function demonstrates **kwargs at its simplest. The ** before user_data tells Python to collect all keyword arguments into a dictionary. When you call build_user(name="Alice", age=30, email="[email protected]"), Python creates user_data = {"name": "Alice", "age": 30, "email": "[email protected]"}. Since we want to return exactly that dictionary, we simply return user_data. The function is flexible—it accepts any keyword arguments without defining them explicitly. You could call it with any combination of keys: build_user(username="bob") or build_user(first="John", last="Doe", city="NYC") all work.

⚠️ Common Mistakes to Avoid

Forgetting the ** in the parameter definition
Trying to access kwargs with dot notation (it's a dict, not object)
Not using .get() for optional keys (causes KeyError)
Expecting kwargs to be ordered in old Python versions
Modifying the original kwargs dict and causing side effects

❓ Frequently Asked Questions

*args captures positional arguments as a tuple. **kwargs captures keyword arguments as a dictionary.

Yes! Order matters: def func(required, *args, **kwargs). *args must come before **kwargs.

Use dictionary methods: kwargs.get('key'), kwargs['key'], or iterate with kwargs.items().

Yes, in Python 3.7+ dictionaries maintain insertion order, so kwargs preserves the order of arguments.

📚 Concepts & Theory

🎯 Your Challenge

📝 Starter Code

Solution

Explanation

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

🔗 Related Exercises

Rest and Spread Operators

Function with Multiple Parameters

Default Parameter Values

Variable Arguments (*args)