Indexing & Slicing

Access single characters or ranges of a string by position.

Syntax

text[index]
text[start:end]

Each character in a string has a position called an index, starting at 0. Negative indexes count from the end, so -1 is the last character.

A slice text[start:end] returns a substring. The character at end is not included. Leave a side blank to go to the beginning or end.

Each character has a positive index from the start and a negative index from the end.

Example

word = 'PYTHON'
print(word[0])
print(word[-1])
print(word[0:3])
print(word[3:])

# Output:
# P
# N
# PYT
# HON

A parser extracts the file extension from a filename string using negative indexing.
A validation function checks the first character of a username to ensure it is a letter.
A data cleaner slices the first 10 characters of a description to create a short preview.

Accesses specific characters using positive (from start) and negative (from end) indices.

text = 'Python'
print(text[0])    # P
print(text[-1])   # n
print(text[2])    # t

Slices the start and end of a URL string using [start:end] notation.

url = 'https://example.com/page'
protocol = url[:5]      # 'https'
path = url[19:]         # '/page'
print(protocol, path)

# Output:
# https /page

Uses the step parameter in slicing to skip characters or reverse the entire string.

s = 'abcdefgh'
print(s[::2])    # aceg  (every other character)
print(s[::-1])   # hgfedcba  (reversed)