Lists

Lists

In this tutorial, we'll store ordered, changeable collections.

A list stores multiple values in order.

names = ["Ada", "Grace", "Linus"]

Lists are useful when you have several related items: names, scores, products, messages, or tasks.

Accessing Items

Python starts counting at 0.

names = ["Ada", "Grace", "Linus"]

print(names[0])
print(names[1])

Output:

Ada
Grace

The first item is at index 0, not index 1.

Changing Lists

Lists are mutable, which means they can change.

tasks = ["wash dishes", "feed cat"]
tasks.append("do homework")

print(tasks)

You can update an item:

tasks[0] = "wash plates"

You can remove an item:

tasks.remove("feed cat")

Looping Over Lists

Lists work well with for loops:

scores = [8, 10, 7]

for score in scores:
    print("Score:", score)

This runs once for each item.

Common Mistake

An index that does not exist causes an error:

names = ["Ada", "Grace"]
print(names[2])  # error

There are only two items, so the valid indexes are 0 and 1.

Checking Before You Access

If you are not sure how long a list is, use len():

names = ["Ada", "Grace"]

print(len(names))

You can use the length to avoid guessing. As a beginner, it is worth printing the list and its length when something feels confusing.

Practice

Create a list of five favourite foods. Print the first item, the last item, then add one more food.