Python Lists

Create, read, change, sort, and safely copy lists of values.

12 min read 10 quiz questions

A list holds a sequence

A list stores values in order. Put items between square brackets, separated by commas.

Positions begin at 0. A negative position counts from the end.

Example 1: create, index, and slice a list

colors = ['red', 'green', 'blue']
print(colors[0])
print(colors[-1])
print(colors[1:])

colors[0] is the first item. colors[-1] is the last item. The slice colors[1:] makes a new list from index 1 to the end.

Change a list

Lists are mutable, which means you can change them after creating them. You can assign to an index or use list methods.

Example 2: add and remove list items

pets = ['cat', 'dog']
pets[1] = 'parrot'
pets.append('fish')
pets.insert(1, 'hamster')
pets.extend(['lizard', 'ant'])
pets.remove('cat')
last_pet = pets.pop()
del pets[1]
print(pets)
print(last_pet)

append() adds one item, insert() adds at an index, and extend() adds every item from another sequence. remove() removes a matching value, pop() removes and returns an item, and del removes by index.

Order and copy lists

Example 3: sort, reverse, and copy

scores = [8, 3, 5]
print(sorted(scores))
scores.sort()
scores.reverse()
copy_scores = scores.copy()
copy_scores.append(10)
print(scores)
print(copy_scores)
print(len(scores))

Tool	What it does	Changes the list?
sorted(items)	Returns a sorted new list	No
items.sort()	Sorts the same list	Yes
items.reverse()	Reverses the same list	Yes
len(items)	Counts items	No

Key points

Lists use square brackets.
Indexes start at zero; -1 is the last item.
Lists can be changed with assignments and methods.
sorted() returns a new list, while sort() changes one.
Use list.copy() to avoid accidental aliasing.

Worked example

A Saturday market list grows and shrinks: add coriander, buy the aubergine off, count what is left.

Example

basket = ["rice", "aubergine"]
basket.append("coriander")
basket.remove("aubergine")
print(basket, len(basket))

How it works, step by step

append() adds to the END.
remove() deletes the first matching VALUE (not position).
len() counts current items.

References & Further Reading

Related entries from PyLabs's own reference library.

copy() (Make a shallow copy of a list.)
append() (Add a single item to the end of the list.)
pop() (Remove and return the item at the specified index.)

Your notes

Practice exercise

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Create numbers = [4, 1, 3]. Append 2, sort the list in place, then print it.

Expected output: [1, 2, 3, 4]

# Write your code below

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Python Lists quiz

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