CODEWITHSUNDEEP
regexpython-3.x
Mithil Bhoras
Mithil Bhoras

Reputation: 904

How does the group in regular expression work when there is only one group?

I did the following:

a = re.compile("(ab*?)")
b = a.search("abbbbbbb")

The following gave me the answer 'a':

b.group(0)

Surprisingly, this also gave me the answer 'a':

b.group(1)

I get a tuple containing only ('a',) when I do this:

b.groups()

If there is only one group, why did it give repeated values for indices 0 and 1? Shouldn't it have raised an IndexError at 1?

Upvotes: 0

Views: 40

Answers (1)

hbgoddard
hbgoddard

Reputation: 148

help(b.group)

Help on built-in function group:

group(...) method of _sre.SRE_Match instance
    group([group1, ...]) -> str or tuple.
    Return subgroup(s) of the match by indices or names.
    For 0 returns the entire match.

Regular expressions start numbering the capture groups at 1. Trying to access group 0 will give you the entire match (all groups), but since the expression has only one group the outputs are the same.

Example:

>>> regex = re.compile("(first) (second)")
>>> results = regex.search("first second")
>>> results.group(1)
'first'
>>> results.group(2)
'second'
>>> results.group(0)
'first second'

Upvotes: 2

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