gh-144694: Fix re.Match.group() doc claiming [1..99] range limit #144696
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The documentation incorrectly stated that numeric group arguments must be in the range [1..99]. This limit was removed in Python 3.5 (bpo-22437). Replace with "a positive integer" since the next sentence already documents the IndexError for out-of-range values.
serhiy-storchaka
added
needs backport to 3.13
| [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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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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_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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You are correct in making that distinction.
LGTM! 👍
3 participants
The documentation for
re.Match.group()incorrectly states that numeric group arguments must be in the inclusive range[1..99]. This limit was removed in Python 3.5 (bpo-22437) when the number of capturing groups became dynamic.Replace
[1..99]with "a positive integer" since the next sentence already documents theIndexErrorfor out-of-range values.📚 Documentation preview 📚: https://cpython-previews--144696.org.readthedocs.build/