Python Basics — Functions

Chapter 13 — Functions

Functions are reusable blocks of code that perform a specific task. They are the building blocks of organized, maintainable programs.

What You’ll Learn

Topic	Page
Defining Functions	Defining Functions →
Parameters & Return	Parameters & Return →
Default & Keyword Args	Default & Keyword Args →
*args & **kwargs	*args & **kwargs →
Docstrings & Annotations	Docstrings & Annotations →
Practice Exercises	Practice Exercises →

Quick Preview

def greet(name, greeting="Hello"):
    """Return a personalized greeting."""
    return f"{greeting}, {name}!"

print(greet("Alice"))             # Hello, Alice!
print(greet("Bob", "Good morning"))  # Good morning, Bob!

Why Functions Matter

Without Functions	With Functions
Code repetition	Write once, use many times
Hard to debug	Isolate and test each piece
Difficult to read	Self-documenting names
Fragile changes	Change one place, fix everywhere

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Start Learning: Defining Functions →