What a Function Really Is: The Specification and Its Four Parts

What are the four parts every function needs — and why does defining one run no code at all until you actually call it?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

0 / 5 passed

Exercise 1 of 5

Your first function

Define a function named square that takes one number n and gives back that number multiplied by itself. You don't have to call it — the checks call square with several inputs for you.

def square(n):
    # your code here — give back n times itself
    ...

def square(n):
    # your code here — give back n times itself
    ...

Python runs in your browser

⌘/Ctrl + Enter runs

is a function defined with def

squares a positive number

handles zero and negative numbers

←Previous Abstraction and Decomposition: Why Your Phone Is a Black Box Next Writing Your First Function: From a Sentence to is_even →