Question

In the snippet below, the non-capturing group "(?:aaa)" should be ignored in the matching result,

The result should be "_bbb" only.

However, I get "aaa_bbb" in the matching result; only when I specify group(2) does it show "_bbb".

>>> import re
>>> s = "aaa_bbb"
>>> print(re.match(r"(?:aaa)(_bbb)", s).group())

aaa_bbb

Answer 1

group() and group(0) will return the entire match. Subsequent groups are actual capture groups.

>>> print (re.match(r"(?:aaa)(_bbb)", string1).group(0))
aaa_bbb
>>> print (re.match(r"(?:aaa)(_bbb)", string1).group(1))
_bbb
>>> print (re.match(r"(?:aaa)(_bbb)", string1).group(2))
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
IndexError: no such group

If you want the same behavior than group():

" ".join(re.match(r"(?:aaa)(_bbb)", string1).groups())