Free course · Lesson 3 of 5

Functions & Scope

In this lesson you will

Define a function with parameters and a return value
Reuse one function for different inputs

A function packages a piece of logic under a name so you can reuse it instead of copy-pasting code. Python functions can take parameters, return a value with return, and even provide sensible defaults.

def greet(name): defines a function; greet("Grace") calls it.
Default parameters: def greet(name="friend"): makes an argument optional.
Variables created inside a function are local — they don't leak outside it.
Good function names and single responsibilities make code easier to test and debug.

💡 Practical Skill: Break a big task (like generating an invoice) into small, named functions — calculate_total(), apply_discount(), format_receipt() — each easy to test on its own.

Worked exampleReusable Discount Calculator

Python

def calculate_total(price, quantity, discount_percent=0):    subtotal = price * quantity    discount = subtotal * (discount_percent / 100)    return subtotal - discount # Reuse the same function for different ordersorder_1 = calculate_total(price=2500, quantity=3)order_2 = calculate_total(price=2500, quantity=10, discount_percent=15) print(f"Order 1 total: {order_1} SSP")print(f"Order 2 total (bulk discount): {order_2} SSP")

Practice exercise

Write convert_to_usd(amount_ssp, rate) and use it for three amounts.

Key takeaways

return hands a value back; print only displays it
Default arguments make parameters optional
Good names describe what a function does

In the full program Module 4: Writing Reusable Functions See how this topic is taught in depth, with practical activities and an assessment.

Free self-study lesson — no certificate. For the full instructor-led program, see registration options.