Multiple capturing groups within non-capturing group using Python regexes

Question

I have the following code using multiple capturing groups within a non-capturing group:

>>> regex = r'(?:a ([ac]+)|b ([bd]+))'
>>> re.match(regex, 'a caca').groups()
('caca', None)
>>> re.match(regex, 'b bdbd').groups()
(None, 'bdbd')

How can I change the code so it outputs either ('caca') or ('bdbd')?

Answer 1

You are close.

To get the capture always as group 1 can use a lookahead to do the match and then a separate capturing group to capture:

(?:a (?=[ac]+)|b (?=[bd]+))(.*)

Demo

Or in Python3:

>>> regex=r'(?:a (?=[ac]+)|b (?=[bd]+))(.*)'
>>> (?:a (?=[ac]+)|b (?=[bd]+))(.*)
>>> re.match(regex, 'a caca').groups()
('caca',)
>>> re.match(regex, 'b bdbd').groups()
('bdbd',)