Day 14/100: Understanding *args and **kwargs in Python Functions

Welcome to Day 14 of the 100 Days of Python series!
Today we’re going to unlock the magic behind flexible function arguments — *args and `kwargs`. These let your functions accept **any number of arguments, making your code more dynamic, reusable, and powerful.

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📦 What You’ll Learn

• What *args and **kwargs are
• When and how to use them
• How to combine them with regular arguments
• Real-world examples

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🧠 1. What Are *args?

*args lets your function accept any number of positional arguments as a tuple.

🔸 Example:

def add_numbers(*args):
    total = sum(args)
    print("Sum:", total)

add_numbers(1, 2)
add_numbers(10, 20, 30)

Output:

Sum: 3
Sum: 60

You can loop through args like a list:

def show_args(*args):
    for arg in args:
        print(arg)

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🧠 2. What Are **kwargs?

**kwargs lets your function accept any number of keyword arguments (named arguments) as a dictionary.

🔸 Example:

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

print_info(name="Alice", age=30, city="New York")

Output:

name: Alice
age: 30
city: New York

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🧪 3. Using Both Together

You can use *args and **kwargs in the same function:

def demo_function(*args, **kwargs):
    print("Positional arguments:", args)
    print("Keyword arguments:", kwargs)

demo_function(1, 2, 3, name="Alice", job="Engineer")

Output:

Positional arguments: (1, 2, 3)
Keyword arguments: {'name': 'Alice', 'job': 'Engineer'}

🔺 Always put *args before **kwargs in the function definition.

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✨ 4. Default + Flexible Parameters

You can mix regular, *args, and **kwargs:

def send_email(to, subject, *attachments, **headers):
    print("To:", to)
    print("Subject:", subject)
    print("Attachments:", attachments)
    print("Headers:", headers)

send_email(
    "[e-mail]",
    "Meeting Notes",
    "file1.pdf", "file2.png",
    priority="high", read_receipt=True
)

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🔄 5. Unpacking with * and **

You can pass a list or dictionary into a function using * and **:

def greet(name, age):
    print(f"Hello {name}, you're {age} years old.")

info = {"name": "Bob", "age": 25}
greet(**info)  # Unpacks dictionary as keyword arguments

nums = [5, 10]
def multiply(x, y):
    print(x * y)

multiply(*nums)  # Unpacks list as positional arguments

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🎯 Real-World Example: Logging

def log_event(event_type, *args, **kwargs):
    print(f"[{event_type.upper()}]")
    for arg in args:
        print(f"- Detail: {arg}")
    for key, val in kwargs.items():
        print(f"- {key}: {val}")

log_event(
    "error",
    "File not found", "User logged out",
    filename="report.pdf", user="admin"
)

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🧼 Best Practices

• ✅ Use *args when you’re not sure how many positional arguments will be passed.
• ✅ Use **kwargs to accept any number of named arguments.
• ✅ Use descriptive names instead of just args and kwargs for clarity (e.g., *numbers, **options).
• ⚠️ Don’t overuse them where explicit parameters make more sense.

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🧠 Recap

Today you learned:

• How *args collects extra positional arguments
• How **kwargs collects extra keyword arguments
• How to combine them with regular parameters
• How to unpack values using * and **
• Real-world examples like logging and flexible APIs

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