Clash Royale CLAN TAG#URR8PPP

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?

group()

If a group number is negative or larger than the number of groups defined in the pattern, an IndexError exception is raised.

1 Answer
1

help(b.group)

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'


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