Functions, Parameters & Return Values — Lesson 1: Returning an answer

New skill: Function definitions and return
Previously learned: Unit 02 — data types, variables, expressions

Why this matters

A function packages instructions into a reusable operation. A function can give a result back with return.

Study this example

def double(n):
    return n * 2

print(double(4))

def starts a function definition. Its indented body runs when called. return gives a value to the caller. A function with no explicit return produces None.

Before moving on, trace each line of the example by hand. Predict the result before running it in the browser.

Check your understanding

How does double(7) differ from printing the number 14 inside the function?

Common mistake

Printing a value is not the same as returning it.

Practice: Returning an answer

Complete increment_number(number) so it returns number + 1, without printing the answer.

Example 1 — Input

increment_number(4)

Output

5

Example 2 — Input

increment_number(-1)

Output

0

Example 3 — Input

increment_number(99)

Output

100

Starter file: main.py

Use Run to experiment and Check to compare against published examples. A passing public example does not automatically establish mastery.

Hint 1 — Identify the key concept

The input arrives in a parameter called `number`.

Hint 2 — Find an approach

Use addition with the value given to you.

Hint 3 — Check your answer

The grader needs `return`, not `print`.

Reflection

Write a short explanation of why your code works. What input or change would make it behave differently?