Python Functions Explained Simply

June 19, 2026

A function is a named, reusable block of code. Functions keep programs tidy, avoid repetition, and make your code easier to read — all things examiners reward. This guide explains how to write and use them in Python.

Defining a function

def greet():
  print("Hello!")

greet() # calls the function

Parameters: passing in data

Parameters let you give a function information to work with:

def greet(name):
  print("Hello, " + name)

greet("Alice")

Return values: getting data back

Use return to send a result back to wherever the function was called:

def add(a, b):
  return a + b

total = add(3, 4)
print(total) # 7

Why functions matter

• Reuse: write the code once, call it many times.
• Readability: a well-named function explains what code does.
• Decomposition: breaking a big problem into small functions is a key exam skill.

Functions vs procedures

In exam terms, a function returns a value, while a procedure just performs an action (like printing) without returning anything. In Python both are written with def — the difference is whether you use return.

Open the free online Python IDE and try writing a function that returns the area of a rectangle given its width and height. Then check your understanding with our coding challenges.