Find one item.
Take a useful slice.

Indexes select one list item; slices select an ordered part of a list.

01 Learn02 Try03 Predict

01 Learn

Indexes begin at zero, and slices stop before the end.

Use square brackets after a list name to access an item. Positive indexes count from the start; negative indexes count backward from the end.

numbers = [10, 20, 30, 40, 50]
print(numbers[0])
print(numbers[-1])

numbers[0] is the first item and numbers[-1] is the final item.

10
50

A slice uses start:stop:step. The start is included, but the stop position is not included.

↳

Slice boundary: numbers[1:4] contains positions 1, 2, and 3, but not position 4.

Take every second item

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

An omitted start and stop use the full list; step 2 selects every second item.

02 Try

Python Playground

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Try different indexes and slice boundaries. Predict the result before running the code.

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03 Predict

What will this program print?

The stop index is not included in a slice.

letters = ["a", "b", "c", "d", "e"]
print(letters[1:4])

Your learning mentor

Ask Sloby about indexing and slicing

Describe what feels unclear about positions, negative indexes, or slice boundaries.

Hi! I'm Sloby. Let's trace list indexes and slices together.

04 Understanding Check

What will this program print, and why? Explain the negative index and the slice.

scores = [12, 24, 36, 48, 60]

print(scores[-2])
print(scores[1:4])