How to Use *args and **kwargs in Functions

Table Of Contents

• Problem
• Solution
• Explanation

Problem

You need to create functions that accept a variable number of arguments or keyword arguments without knowing the exact count beforehand.

Solution

# *args for variable positional arguments
def sum_numbers(*args):
    return sum(args)

print(sum_numbers(1, 2, 3))        # 6
print(sum_numbers(1, 2, 3, 4, 5))  # 15

# **kwargs for variable keyword arguments
def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

print_info(name="John", age=25, city="NYC")
# name: John
# age: 25
# city: NYC

# Combine regular args, *args, and **kwargs
def flexible_function(required, *args, **kwargs):
    print(f"Required: {required}")
    print(f"Args: {args}")
    print(f"Kwargs: {kwargs}")

flexible_function("hello", 1, 2, 3, name="Alice", age=30)
# Required: hello
# Args: (1, 2, 3)
# Kwargs: {'name': 'Alice', 'age': 30}

# Unpacking when calling functions
def greet(first, last, age):
    print(f"Hello {first} {last}, age {age}")

person_tuple = ("John", "Doe", 25)
person_dict = {"first": "Jane", "last": "Smith", "age": 30}

greet(*person_tuple)   # Hello John Doe, age 25
greet(**person_dict)   # Hello Jane Smith, age 30

# Practical example: flexible logger
def log_message(level, message, **kwargs):
    print(f"[{level}] {message}")
    if kwargs:
        print(f"Additional info: {kwargs}")

log_message("INFO", "User logged in", user_id=123, ip="192.168.1.1")
# [INFO] User logged in
# Additional info: {'user_id': 123, 'ip': '192.168.1.1'}

# Function wrapper example
def debug_function(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__} with args={args}, kwargs={kwargs}")
        result = func(*args, **kwargs)
        print(f"Result: {result}")
        return result
    return wrapper

@debug_function
def multiply(x, y):
    return x * y

multiply(3, 5)  # Shows debug info + result

Explanation

*args collects extra positional arguments into a tuple. **kwargs collects extra keyword arguments into a dictionary. Use them to create flexible functions.

When calling functions, * unpacks sequences and ** unpacks dictionaries. This pattern is essential for decorators and wrapper functions.