Question

I would like to know the reason behind the following behaviour:

>>> re.compile("(b)").split("abc")[1]
'b'
>>> re.compile("b").split("abc")[1]
'c'

I seems that when I add parentheses around the splitting pattern, re adds it into the split array. But why? Is it something consistent, or simply an isolated feature of regular expressions.

Answer 1

It’s a feature of re.split, according to the documentation:

If capturing parentheses are used in pattern, then the text of all groups in the pattern are also returned as part of the resulting list.

In general, parenthesis denote capture groups and are used to extract certain parts of a string. Read more about capture groups.