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gh-144694: Fix re.Match.group() doc claiming [1..99] range limit #144696

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gh-144694: Fix re.Match.group() doc claiming [1..99] range limit #144696

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8 changes: 4 additions & 4 deletions Doc/library/re.rst
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Expand Up @@ -1407,10 +1407,10 @@ when there is no match, you can test whether there was a match with a simple
result is a single string; if there are multiple arguments, the result is a
tuple with one item per argument. Without arguments, *group1* defaults to zero
(the whole match is returned). If a *groupN* argument is zero, the corresponding
return value is the entire matching string; if it is in the inclusive range
[1..99], it is the string matching the corresponding parenthesized group. If a
group number is negative or larger than the number of groups defined in the
pattern, an :exc:`IndexError` exception is raised. If a group is contained in a
return value is the entire matching string; if it is a positive integer, it is
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@caje731 caje731 Feb 11, 2026

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Actually there seems to be a limit and it can be quantized on one's machine:

>>> import _sre
>>> _sre.MAXGROUPS
1073741823

I see multiple guards in Lib/sre_parse.py that use the MAXGROUPS constant for the upper bound.

Maybe the docs should say in the inclusive range [1.. _sre.MAXGROUPS] or similar?

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@mohsinm-dev mohsinm-dev Feb 11, 2026

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_sre.MAXGROUPS limits the number of groups allowed in a pattern. This is enforced at compile time in _parser.py.

The .group() method itself does not check against _sre.MAXGROUPS. It only checks whether the requested group index is within the number of groups defined in that specific pattern (see match_getindex, where it checks i >= self->groups).

The next sentence in the documentation already explains this clearly:
"If a group number is negative or larger than the number of groups defined in the pattern, an IndexError exception is raised."

Mentioning _sre.MAXGROUPS here would reference a private module and mix two different things:

  • the compile-time limit on total groups in a pattern
  • the runtime behavior of .group().

So I think it is better not to mention _sre.MAXGROUPS in this context.

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@caje731 caje731 Feb 11, 2026

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You are correct in making that distinction.

LGTM! 👍

the string matching the corresponding parenthesized group. If a group number is
negative or larger than the number of groups defined in the pattern, an
:exc:`IndexError` exception is raised. If a group is contained in a
part of the pattern that did not match, the corresponding result is ``None``.
If a group is contained in a part of the pattern that matched multiple times,
the last match is returned. ::
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