Indexing & slicing

A string is a row of characters. Each one has a position called its index, and counting starts at 0:

0P-10

1y-9

2t-8

3h-7

4o-6

5n-5

6i-4

7s-3

8t-2

9a-1

word[0] is the first character, word[-1] the last
word[2:6] is a slice: from index 2 up to, not including, 6
word[::-1] steps backwards, which reverses the string
len(word) is the number of characters

An omitted slice start means "from the beginning": word[:2]. An omitted stop means "to the end": word[-4:]. Multiplying text repeats it: "*" * 3 gives "***".

See it run

word = "planet"
i = 0
i = 3
i = -1
part = word[1:4]

Each letter sits in its own numbered cell, counting from 0. The highlight follows word[i].

Practice indexing & slicing

Exercise 1

With word = "Pythonista" create:

first = the first character
last = the last character (use a negative index)
middle = "thon" (a slice)
backwards = the reversed word

Exercise 2

A shop's product codes look like UK-2026-BLUE. Use slices of code to make:

country = the first 2 characters ("UK")
year = the 4 digits in the middle, as an int (2026)
colour = the last 4 characters, using a negative slice ("BLUE")

Exercise 3

Receipts must hide the card number in the code editor below except its last 4 digits.

last4 = the last 4 characters of card
masked = one * for every other digit, followed by last4 (************4444)

Use len(card) so it also works for cards of a different length. The check will try a 15-digit card too.

Free lesson: use the editor to practice it.

Practice

Loading Python…

Loading exercise content…

Visualizer Watch your code run line by line

Run your code, then choose Play to follow its execution.

Memory · names → values

Variables appear here as Python creates them.

Output & plots