[New-bugs-announce] [issue32067] Deprecate accepting

[Serhiy Storchaka]

New submission from Serhiy Storchaka <storchaka+cpython at gmail.com>:

Currently `{m}`, `{m,n}`, `{m,}` and `{,n}` where m and n are non-negative decimal numbers are accepted in regular expressions as quantifiers that mean repeating the previous RE from m (0 by default) to n (infinity by default) times.

But if the opening brace '{'is not followed by one of the above patterns, it means just the literal '{'.

>>> import re
>>> re.search('(foobar){e}', 'xirefoabralfobarxie')
>>> re.search('(foobar){e}', 'foobar{e}')
<re.Match object; span=(0, 9), match='foobar{e}'>

This conflicts with the regex module which uses braces for defining the "fuzzy" matching.

>>> import regex
>>> regex.search('(foobar){e}', 'xirefoabralfobarxie')
<regex.Match object; span=(0, 6), match='xirefo', fuzzy_counts=(6, 0, 0)>
>>> regex.search('(foobar){e}', 'foobar{e}')
<regex.Match object; span=(0, 6), match='foobar'>

I don't think it is worth to add support of fuzzy matching in the re module, but for compatibility it would be better to raise an error or a warning in case of '{' not following by the one of the recognized patterns. This could also help to catch typos and errors in regular expressions, i.e. in '-{1.2}' or '-{1, 2}' instead of '-{1,2}'.

Possible variants:

1. Emit a DeprecationWarning in 3.7 (and 2.7.15 with the -3 option), raise a re.error in 3.8 or 3.9.

2. Emit a PendingDeprecationWarning in 3.7, a DeprecationWarning in 3.8, and raise a re.error in 3.9 or 3.10.

3. Emit a RuntimeWarning or SyntaxWarning in 3.7 and forever.

4. Emit a FutureWarning in 3.7, and implement the fuzzy matching or replace re with regex sometimes in future. Unlikely.

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assignee: serhiy.storchaka
components: Library (Lib), Regular Expressions
messages: 306479
nosy: ezio.melotti, mrabarnett, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Deprecate accepting
type: enhancement
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue32067>
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