Python Basics · Functions · Lesson 11 of 36
Defining Functions
Concept
Defining Functions
Functions are defined with def, and Python uses indentation to mark what is inside the function body.
A function without an explicit return statement returns None automatically, the same way JavaScript functions return undefined by default.
- Explain the core idea behind Defining Functions.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Defining Functions. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Write a function square(n) that returns n squared.
Ask about this lesson or your next move. The guide explains the path without taking the work away from you.
Ready for the next lesson?
Mark this lesson complete when you have finished the exercise.
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