Lists

A list is an ordered collection of values that you can grow, shrink, and rearrange after it's created — the closest thing Python has to an actual grocery list.

Creating a list and reading from it

Square brackets with commas between items make a list. Items are numbered starting at 0, and a negative index counts from the end:

groceries = ["milk", "eggs", "bread", "spinach"]
print(groceries[0])
print(groceries[-1])
print(len(groceries))

milk
spinach
4

Adding, removing, and changing items

Unlike a string, a list can be changed in place. .append() adds to the end, .remove() deletes the first matching value, and assigning to an index overwrites what's there:

groceries.append("cheese")
groceries.remove("bread")
groceries[0] = "oat milk"
print(groceries)

['oat milk', 'eggs', 'spinach', 'cheese']

Walking through it: append("cheese") tacks cheese on the end, remove("bread") drops bread wherever it was sitting, and groceries[0] = "oat milk" swaps out whatever was first — which by then was still "milk" — for "oat milk".

Slicing out a range of items

The same [start:end] slicing you saw with strings works on lists too, and it always hands back a new list rather than a single value:

numbers = [10, 20, 30, 40, 50]
print(numbers[1:3])
print(numbers[:2])
print(numbers[2:])

[20, 30]
[10, 20]
[30, 40, 50]

Leaving out the start means "from the beginning"; leaving out the end means "through the end."

Sorting and summing

prices = [4.5, 2.0, 6.25, 1.75]
prices.sort()
print(prices)
print(sum(prices))

[1.75, 2.0, 4.5, 6.25]
14.5