python - What does "(?u)" do in a regex? -

i looked how tokenization implemented in scikit-learn , found regex (source):

token_pattern = r"(?u)\b\w\w+\b" 

the regex pretty straightforward have never seen (?u) part before. can explain me part doing?

it switches on re.u (re.unicode) flag expression.

from module documentation:

(?ilmsux)

(one or more letters set 'i', 'l', 'm', 's', 'u', 'x'.) group matches empty string; letters set corresponding flags: re.i (ignore case), re.l (locale dependent), re.m (multi-line), re.s (dot matches all), re.u (unicode dependent), , re.x (verbose), entire regular expression. (the flags described in module contents.) useful if wish include flags part of regular expression, instead of passing flag argument re.compile() function.