[New-bugs-announce] [issue42871] Regex compilation crashed if I change order of alternatives under quantifier

[Renji]

New submission from Renji <AsoRenji at gmail.com>:

I can compile "((a)|b\2)*" expression and this expression successfully return captures from first repetition and second repetition in one time. But if I write (b\2|(a))* expression, I get "invalid group reference 2 at position 3" error. Either first or second behavior incorrect.
python3 --version Python 3.7.3

import re
text="aba"
#match=re.search(r"(b\2|(a))*",text) - not worked
match=re.search(r"((a)|b\2)*",text)
if(match):
    #show aba ba a
    print(match.group(0)+" "+match.group(1)+" "+match.group(2))

----------
components: Regular Expressions
messages: 384703
nosy: Renji, ezio.melotti, mrabarnett
priority: normal
severity: normal
status: open
title: Regex compilation crashed if I change order of alternatives under quantifier
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42871>
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