regex: Improper handling of Unicode Properties in character set 3.16a2

Aperta
  • Qualcosa non va?
#161,814 1 commento 0 reazioni 0 assegnatari Vedi su GitHub

I maintainer di solito rispondono entro 1 giorno

Nessuno ha ancora preso questa issue.

Valutazione

Difficoltà
4/5
Tempo stimato
3-5 giorni
Idoneità per principianti
56/100
Tipo di issue
Bug
Chiarezza
Specificata chiaramente
Stato di attività
Attiva
Stack tecnologico
python
Ambito
backend

Direzione di ricerca

Start in Lib/re/_compiler.py at _optimize_charset() and inspect how IN_UNI_IGNORE handles category items when a set contains cased literals or ranges. Use the examples in the issue as regression cases, then run the relevant regular expression tests. Done means the category properties and their negations preserve the reported IGNORECASE behavior while existing set matching continues to work.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

type-bug
Bug report

I found this when evaluating the Unicode Properties in the recent alpha release for Re. I realize this work is a WIP, but figured I'd share in case this issue wasn't already known.

With re.IGNORECASE, a character set that contains a case-sensitive property escape (\p{Lu}, \p{Lt}, \p{Uppercase}, \p{Lowercase}, or their \P{...} forms) together with a cased literal or range gives the wrong results. Adding a member to a set can remove matches:

>>> import re
>>> re.fullmatch(r'[\p{Lu}]', 'A', re.IGNORECASE)
<re.Match object; span=(0, 1), match='A'>
>>> re.fullmatch(r'[\p{Lu}x]', 'A', re.IGNORECASE)    # expected a match
>>> re.fullmatch(r'[\p{Lu}x]', 'A')
<re.Match object; span=(0, 1), match='A'>

Below is info gathered by AI, hopefully it is helpful, but the important part is the behavior that doesn't match expectations.

More examples, all with re.IGNORECASE:

Pattern String Result Expected
[\p{Lu}x] 'A' no match match
[\p{Lu}a-c] 'Z' no match match
[^\p{Lu}x] 'A' match no match
[\P{Lu}x] 'A' match no match
[\p{Lt}x] 'Dž' no match match
[\p{Uppercase}x] 'A' no match match
[\p{Lowercase}x] 'A' match no match

"Expected" is how these properties already behave with IGNORECASE outside a set, or as the only member of a
set: \p{Lu} and [\p{Lu}] match 'A' but not 'a'.

The same happens with an inline (?i:...), and with re.ASCII | re.IGNORECASE for ASCII characters. Sets without
a cased literal or range, such as [\p{Lu}1] and [\p{Lu}\d], are not affected.

Cause: in Lib/re/_compiler.py, when a set under IGNORECASE contains a cased literal or range (hascased
from _optimize_charset()), the whole set is compiled as IN_UNI_IGNORE (IN_IGNORE with ASCII). Those
opcodes lowercase the character before testing it against every item in the set, including CATEGORY items. The
literals in the set are already lowercased, so they still match correctly, but the categories are now tested
against the lowercased character: 'A' becomes 'a' before the Lu test.

For the categories that existed before 3.16 (\d, \s, \w), lowercasing a character never changes whether it is
in the category, so this was harmless. It does for the new CATEGORY_LU, CATEGORY_TITLE, CATEGORY_UPPER and
CATEGORY_LOWER, and their negations. Checking every code point that changes when lowercased, these are the only
supported properties whose membership changes (Lu, Lt, Uppercase, Lowercase).

A fix could test CATEGORY items against the original character rather than the lowercased one in the
ignore-case set opcodes, or have the compiler keep those categories out of the ignore-case check.

CPython versions tested on:

3.16

Operating systems tested on:

macOS

Lingua principale
Python
Stelle
78.2k
Fork
36.6k
Merge medio
19h 57m
PR unite (30g)
630

Preparare l'ambiente

Apri in Codespaces

Avvia il container di sviluppo del progetto nel browser, con il tuo account GitHub.

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

Altre issue di python/cpython

Tutte le issue di python/cpython

Issue simili

Altre issue su Python

Ricevi le nuove issue nella tua casella

Un breve riepilogo di issue GitHub adatte ai principianti.