Functions

Introduction

Functions are the building blocks of reusable code. Python functions are defined with the def keyword and support powerful features like default arguments, keyword arguments, and more.

Defining functions

def greet(name):
    """Greet someone by name."""
    return f"Hello, {name}!"

print(greet("Alice"))  # "Hello, Alice!"

# Default parameters
def power(base, exponent=2):
    return base ** exponent

power(3)     # 9
power(3, 3)  # 27

# *args and **kwargs
def flexible(*args, **kwargs):
    print(f"Args: {args}")
    print(f"Kwargs: {kwargs}")

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

# Lambda functions (anonymous)
square = lambda x: x ** 2
numbers = [3, 1, 4, 1, 5]
sorted_nums = sorted(numbers, key=lambda x: -x)  # [5, 4, 3, 1, 1]

Docstrings

Always document your functions with docstrings. They describe what a function does and can be accessed via help().

def calculate_area(radius):
    """Calculate the area of a circle.
    
    Args:
        radius: The radius of the circle.
        
    Returns:
        The area as a float.
    """
    import math
    return math.pi * radius ** 2

Assignment