Python regex - why does end of string ($ and \Z) not work with group expressions?

Question

In Python 2.6. it seems that markers of the end of string $ and \\Z are not compatible with group expressions. Fo example

import re         


        

Answer 1

A [..] expression is a character group, meaning it'll match any one character contained therein. You are thus matching a literal $ character. A character group always applies to one input character, and thus can never contain an anchor.

If you wanted to match either a whitespace character or the end of the string, use a non-capturing group instead, combined with the | or selector:

r"\w+(?:\s|$)"

Alternatively, look at the \b word boundary anchor. It'll match anywhere a \w group start or ends (so it anchors to points in the text where a \w character is preceded or followed by a \W character, or is at the start or end of the string).