Functions and Scope

Functions are reusable blocks of code that perform a specific task. They help you organise your code, avoid repetition, and make programs easier to read, test, and maintain. Functions are one of the most important concepts in programming.

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Defining a Function

Use the def keyword:

def greet(name):
    """Greet a person by name."""
    print(f"Hello, {name}!")

# Call the function
greet("Alice")   # Hello, Alice!
greet("Bob")     # Hello, Bob!

Anatomy of a function:

• def — keyword to define a function
• greet — the function name
• (name) — parameter(s)
• """ docstring """ — optional documentation
• The indented block — the function body
• Call with greet("Alice")

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Return Values

Functions can return values using the return statement:

def add(a, b):
    """Return the sum of a and b."""
    return a + b

result = add(3, 5)
print(result)  # 8

# Functions without return statement return None
def say_hello():
    print("Hello!")

x = say_hello()  # prints "Hello!"
print(x)          # None

Returning Multiple Values

def get_stats(numbers):
    """Return the min, max, and average of a list."""
    return min(numbers), max(numbers), sum(numbers) / len(numbers)