Lesson 8: Functions – Defining & Using

1. What are Functions?

Functions are reusable blocks of code — like mini-programs.

Why use them?

• Avoid repeating code
• Make code organized & readable
• Essential in ML (loss functions, models, training loops)

Define with def:

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

Call it: greet("Alex") → Hello, Alex!

2. Return Values

Functions can return results with return.

def add(a, b):
    return a + b

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

Multiple returns possible, but usually one.