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F3.3 Lists: one-dimensional arrays

Strings, lists and records · GCSE · OCR J277 2.2.3, AQA 8525 3.2.6, Edexcel 1CP2 6.3.1 · about 15 min

BugBotLab

What this lesson is about

Making, indexing and changing a list; append, remove, in, split and join.

Questions 6 marks in all

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

    legs = [20, 15, 30]
print(legs[0], legs[-1], len(legs))
    Answer:
    20 30 3

    Index 0 is the first item, -1 the last, and len counts the items.

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

    notes = [262, 294, 330]
notes[0] = 523
notes.append(349)
print(notes)
    Answer:
    [523, 294, 330, 349]

    Assigning to an index replaces that item; append adds one to the end.

  3. [1 mark]legs = [20, 15, 30]. What happens with print(legs[3])?

    1. AIndexError: there is no index 3
    2. BIt prints 30
    3. CIt prints 0
    4. DIt prints None
    Answer: A. Three items have indexes 0, 1 and 2.

  4. [1 mark]Why use an array rather than separate variables such as reading1, reading2, reading3?

    1. AOne name holds them all, and a loop can process every item
    2. BArrays use less electricity
    3. CSeparate variables cannot hold numbers
    4. DArrays are always sorted
    Answer: A. An array groups values under one identifier, so the same code works however many values there are.

  5. [1 mark]What does this program print?

    sides = "30,20".split(",")
print(sides)
print(int(sides[0]) + int(sides[1]))
    Answer:
    ['30', '20']
50

    split makes a list of strings; int is needed before adding them.

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

    colours = ["red", "green"]
print("green" in colours, colours.index("green"))
    Answer:
    True 1

    in asks whether an item is in the list, and index gives its position.

The task: a changing tune

Start with notes = [262, 294, 330]. Change the first note to 523, add 349 to the end, print how many notes there are as 4 notes, then play every note in the list for 0.3 seconds. Change the list with list operations, not by typing a new list.

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

notes = [262, 294, 330]

The hint students can ask for: A list can be changed in place: replace one item by its position, and add another on the end. Then loop over the list to play it.

A solution

from bugbot import *
connect()
notes = [262, 294, 330]
notes[0] = 523
notes.append(349)
print(len(notes), "notes")
for note in notes:
    tone(note, 0.3)

Any program that meets the task's checks is marked correct in the simulator; this is one way, not the only way.