The groups() method in regular expressions in Python

Question

I am learning about regex in Python and I have problems understanding the function groups().

>>> m = re.match("([abc])+", "abc")

Here I have defined the class [abc], which as I know, means any of the characters a to c. It's defined inside a group and the + sign means we want at least one of such groups. So I execute the following line and the result is understandable:

>>> m.group()
'abc'
>>> m.group(0)
'abc'

I get why this happens. The index of the main group is 0 and 'abc' matches the class we have defined. So far so good, but I don't get why the following lines get executed the way they do:

>>> m.group(1)
'c'
>>> m.groups()
('c',)

What is group(1), I have only defined one group here and why the groups function has only the character 'c' in it? Isn't it supposed to return a tuple containing all the groups? I'd suppose it would at least contain 'abc'.

Answer 1

For re details consult docs. In your case:

group(0) stands for all matched string, hence abc, that is 3 groups a, b and c

group(i) stands for i'th group, and citing documentation

If a group matches multiple times, only the last match is accessible

hence group(1) stands for last match, c

Your + is interpreted as group repetation, if you want repeat [abc] inside group, move + into parentheses:

>>> re.match("([abc])", "abc").groups()
('a',)
>>> re.match("([abc]+)", "abc").groups()
('abc',)