"Ain't ain't a word 'cause it don't match the regex."

BTW, should be "\b\w+\b". The \b is a zero-width match for the start or end of a word. Your pattern requires a space before and after:

  >>> import re
  >>> re.compile(r"\b\w+\b").findall("What's the problem?")
  ['What', 's', 'the', 'problem']
  >>> re.compile(r"\s\w+\s").findall("What's the problem?")
  [' the ']

  cljs.user> (re-seq #"\s\w+\s" "やり直して")
  nil

Joking aside, is it common to use regular expressions? Seems like the method only works for languages with spaces. I think a more sophisticated lexer may be necessary, but are there are non-regex, "fast approximations" that work across most languages? This is a problem that I have not tried solving before.