Lists and indexing

A list stores values in order. Indexes start at 0, so the first item is at index 0. Negative indexes count back from the end. Lists are mutable: you can replace or append items.

minutes = [20, 25, 30]
print(minutes[0])
print(minutes[-1])
minutes[1] = 35
minutes.append(40)
print(minutes)

20
30
[20, 35, 30, 40]

Use a list in a loop

A for loop can visit each value directly. len() reports how many items the list contains.

minutes = [20, 25, 30]
for value in minutes:
    print(value)
print(len(minutes))

20
25
30
3

Why this works

A list keeps an ordered sequence, so its position has meaning. The first item uses index 0, the second index 1, and index -1 accesses the last item. Assigning to an existing index replaces one value; append() adds a new value at the end.

Practice

Create a list of three study subjects. Print the first and last items, replace the middle item, then append a fourth subject.

Try another case

After values = [5, 10] and values.append(15), what are values[1] and values[-1]?