Strings: Indexing & Length

A string is a sequence of characters. Each position has an index — and Python counts from zero:

word = "Python"
word[0]    # 'P'  (first!)
word[5]    # 'n'  (last)
word[6]    # IndexError — only 0..5 exist

Negative indices count from the end: word[-1] is 'n', word[-2] is 'o'.

Length

len() counts characters: len("Python") is 6.

Strings are immutable

You cannot change a character in place: word[0] = "J" raises TypeError. Instead, build a new string — the next lesson shows slicing, and methods give you more tools.