Strings and indexing

A string is a sequence of one or more Unicode characters: letters, digits, spaces or symbols. It is written in single, double or triple quotes: 'India', "India" or '''India'''. Triple quotes let a string run over several lines.

Each character has a position number, its index. The first character has index 0, and the last has index n - 1, where n = len(string), the length. For s = 'Namaste India' (13 characters, counting the space), s[0] is 'N' and s[8] is 'I'.

• An index outside this range gives an IndexError.
• The index must be an integer: s[1.5] gives a TypeError.
• It can be an expression, worked out first: s[2 + 4] is the same as s[6].

Negative indices count from the right: -1 is the last character, and -n the first. For s = 'Namaste India', s[-1] is 'a' and s[-13] is 'N'.

Python has no separate character type: a single character is just a string of length 1.

Strings are immutable: once made, they cannot be changed. Trying s[0] = 'M' gives TypeError: 'str' object does not support item assignment. To 'change' a string, you build a new one.