lesson.md

Lesson 4.02: For Loops Using Range

Learning Objectives

Students will be able to...

• Define and identify: range.
• Use the range and len function to to update lists via for loops.

Materials/Preparation

• 4.02 Slide Deck
• Do Now
• Lab - Getting Loopy (docx) (pdf)
• Associated Reading
• Read through the Do Now, lesson, and lab so that you are familiar with the requirements and can assist students.

Pacing Guide

Duration	Description
5 Minutes	Do Now
10 Minutes	Lesson
35 Minutes	Lab
5 Minutes	Debrief

Instructor's Notes

1. Do Now

• Display the Do Now on the board.
• Students experiment with and are introduced to the range function.

2. Lesson

Part 1 of the Do Now

• Ask students what the range function did.
• Remind them that there are reference docs online.
• Show the docs for the range function. Note that it can take in a third value that is optional.
• Work together with the students to write a for loop using the range function.

Part 2 of the Do Now

• Ask the students what happened
• Ask the students why these values might be helpful
• They are a list of the indices!

Part 3 of the Do Now (many students likely didn't finish)

• Ask students to write the first line of the loop on the board
• Work together as a class to come to a solution that is demonstrated for all to see.

Debugging Loops

In the sample "Function Contains Two Errors" code, we expect the return value True, but we get an IndexError instead.

Suggest printing the values of the indices immediately before the line where the error appears (right after while statement).

First error: the index of the last character is 3, so the initial value for j should be different: j = len(word2)-1.

Second error: we need to include the character at index 0, so we need to change the while condition: while j >= 0:

3. Lab

• Students re-write the fruit pluralize program from yesterday's do now, but without creating a new list.
• Students write a function that reverses the letters in a string.

4. Debrief

• Talk about any issues the students had with the lab today.
• Discuss how lists are mutable, so you don't have to return a new value. Instead, the list is just updated as the loop runs.

Video explanation on Python Lists being Mutable

Accommodation/Differentiation

• If students are having a hard time with the fruit pluralize, consider altering the fruit program to not allow fruit that ends in y.
• Some students may have issues with grabbing the last item of a string, consider providing tips or scaffolding for students that are struggling with this.
• Go over the bonus question if any students got to it. Discuss having a function inside of the loop and how that operated.