Chapter 8a - Lists

A list is an ordered collection. Use square brackets. Indexing starts at 0.

scores = [90, 85, 100]
names = ["Ada", "Lin", "Grace"]
mixed = [1, "two", True]
empty = []

🧪 Try it yourself

Change the list and print a different index.

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Indexing and slicing

Expression	Meaning
items[0]	First element
items[-1]	Last element
items[1:3]	From index 1 up to (not including) 3
len(items)	How many elements

🧪 Slicing

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Mini quiz — lists and indexes

Quiz

Lists and indexes

1 / 2

What is fruits[1]?

fruits = ["apple", "banana", "cherry"]

Pick an answer to see if you are right.

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Challenge: first and last

Write ends(items) so it returns a new list with only the first and last values.

items	Return
[3, 1, 4, 1, 5]	[3, 5]
["a", "b"]	["a", "b"]

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Changing a list

Common methods:

Method	Effect
items.append(x)	Add x at the end
items.pop()	Remove and return the last item
items.insert(i, x)	Put x at index i
items[i] = x	Replace the value at index i

🧪 Growing a list

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Looping through a list

for item in names:
    print(item)

for i in range(len(names)):
    print(i, names[i])

🧪 Loop

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Mini quiz — mutate and loop

Quiz

Mutate and loop

1 / 2

What is nums after this?

nums = [1, 2]
nums.append(3)

Pick an answer to see if you are right.

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Challenge: sum of a list

Write total(nums) so it returns the sum of all numbers. Do not use sum().

nums	Return
1 2 3	6
10 -2 4	12

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Exercises

Activity: Largest number

Write largest(nums) so it returns the biggest value. Assume the list is not empty. Do not use max().

Expected for 3 9 2 9:

9