Regular expressions

The re module compiles a pattern and applies it to text. search finds the first match, findall returns every match, sub replaces them. Write patterns as raw strings (r"...") so backslashes survive.

Groups in parentheses capture parts of a match, and named groups make the result readable.

Building blocks worth memorising: \d digit, \w word character, \s whitespace, + one or more, * zero or more, ? optional, ^ start, $ end, [] a set, | alternatives.