Worksheet

F3.4 Iterating over a list

Strings, lists and records · GCSE · OCR J277 2.2.3, AQA 8525 3.2.6, Edexcel 1CP2 6.2.2 · about 15 min

What this lesson is about

Loops over items and indexes, totals, counts, min and max, and linear search.

• for over the items
• for over the indexes
• The patterns, over a list
• Readings from the robot
• Searching a list

Questions 6 marks in all

1. [1 mark]What does this program print?

   total = 0
   for r in [4, 7, 9]:
       total = total + r
   print(total / 3)

2. [1 mark]What does this program print?

   colours = ["red", "green", "blue"]
   for i in range(len(colours)):
       print(i, colours[i])

3. [1 mark]What does this program print?

   readings = [41, 35, 30, 25]
   count = 0
   for r in readings:
       if r < 32:
           count = count + 1
   print(count)

4. [1 mark]A linear search finds its target at index 2. Why does it use break?

   1. AThere is no need to look at the rest of the list
   2. BTo restart the search
   3. Cbreak is needed in every loop
   4. DTo print the index

5. [1 mark]How does a linear search work?

   1. AIt checks each item in turn, from the start, until it finds the target or runs out
   2. BIt jumps to the middle and halves the list
   3. CIt sorts the list first
   4. DIt only checks the first and last items

6. [1 mark]What does this program print?

   readings = [40, 36, 25]
   for i in range(1, len(readings)):
       print(readings[i - 1] - readings[i])

The task: sensor log

Drive forward in five steps of 8 cm, recording distance() before each step in a list. Then print four lines: readings: <the list>, smallest: <cm>, largest: <cm> and average: <cm>. Work the average out with a loop or with sum and len, not by typing numbers.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

readings = []

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/f3-4-iterating-over-a-list/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Find the smallest reading with a loop, without using min.
2. Drive a shape from a list of [distance, turn] pairs, such as [[30, 90], [20, 90], [30, 90], [20, 90]].
3. Count how many names in a list start with the letter A.