Python Functions – Organizing and Reusing Your Code

Functions are reusable blocks of code that perform specific tasks. They help organize your programs and avoid repeating the same code multiple times.

Creating a Function

Use the def keyword to create a function:

def greet():
    print("Hello, World!")

# Call the function
greet()  # Output: Hello, World!

Functions with Parameters

Parameters allow functions to work with different inputs:

def greet_person(name):
    print(f"Hello, {name}!")

greet_person("Alice")  # Hello, Alice!
greet_person("Bob")    # Hello, Bob!

Functions with Return Values

Functions can return results for later use:

def add_numbers(a, b):
    result = a + b
    return result

sum_result = add_numbers(5, 3)
print(sum_result)  # 8

Default Parameters

Provide default values for parameters:

def introduce(name, age=25):
    print(f"Hi, I'm {name} and I'm {age} years old.")

introduce("Charlie")      # Uses default age
introduce("Diana", 30)    # Uses provided age

Multiple Return Values

Python functions can return multiple values:

def calculate(a, b):
    sum_val = a + b
    diff_val = a - b
    return sum_val, diff_val

result1, result2 = calculate(10, 3)
print(result1)  # 13
print(result2)  # 7

Function Best Practices

Write clear, focused functions that do one thing well:

def calculate_area(length, width):
    """Calculate the area of a rectangle."""
    return length * width

area = calculate_area(5, 3)
print(f"Area: {area} square units")

Functions make your code modular, easier to test, and more maintainable.