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Year 9 · Autumn 1 · Python II: lists and strings

Lists: creating and indexing

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What this lesson covers

Topic 14 Programming further

KS3 Computing · Real programs keep data in lists, take text apart as strings, split work into subroutines, check their input, save to files, and get tested on purpose.

ProgrammingCambridge Lower Secondary Computing 0860

You will learn to

  • Create a Python list with square brackets and print one item using its index.
  • Explain why the first item is at index 0 and the last is at len(list) - 1.
  • Use a negative index, like -1, to get the last item.
  • Explain the error that an index past the end of the list gives.

Success criteria

  • I can print the first and the last item of my shopping list.
  • I can say which index holds the 4th item in a list.
  • I can explain 'list index out of range' in my own words.

Key words

Say each word, then read what it means. Every one is in the glossary too.

list
One name holding many values in order. Also called an array.
index
An item's position in a list, counting from 0.
Subroutine
A named block of code you can call when needed.
Function
A subroutine that returns a value.
Parameter
A placeholder in a subroutine for a value passed in.
Validation
Checking input is reasonable before using it.
Boundary data
Test data at the very edge of what's allowed.

The explanation

Read it here, or open the study page below to go one step at a time with things to try.

Lists

A list (or array) stores many values under one name, in order.

scores = [12, 45, 33, 50]
Index0123
Value12453350
?Why?

Why start at 0? The index means 'how many steps from the start'. The first item is 0 steps away.

  • scores[0] → 12
  • scores[-1] → 50 (the last one)
  • scores.append(28) adds to the end
  • len(scores) → how many items
  • scores[10] → error: no item there

Study it

Open the study page and go one step at a time.

Topic 14 · Year 9

Programming further

Real programs keep data in lists, take text apart as strings, split work into subroutines, and get tested on purpose.

Check yourself

One question at a time. The reason shows after each answer.

Saved on this device.