New submission from David Ellsworth <david...@earthling.net>:
The regex /^((x*)\2{3}(?=\2$))*x$/ matches powers of 5 in unary, expressed as
strings of "x" characters whose length is the number.
The following command line should print "1", but prints nothing:
python -c 'import regex; regex.match(r"^((x*)\2{3}(?=\2$))*x$", "x"*125) and
print(1)'
However, this command does print "1":
python -c 'import regex; regex.match(r"^((x*)\2\2\2(?=\2$))*x$", "x"*125) and
print(1)'
And so does this one:
python -c 'import re; re.match(r"^((x*)\2{3}(?=\2$))*x$", "x"*125) and print(1)'
The expression "\2\2\2" should behave exactly the same as "\2{3}", but in the
"regex" module it does not.
Solving the following Code Golf Stack Exchange challenge is what led me to
discover this bug:
https://codegolf.stackexchange.com/questions/211840/is-that-number-a-two-bit-number%ef%b8%8f/222792#222792
----------
components: Regular Expressions
messages: 390175
nosy: Davidebyzero, ezio.melotti, mrabarnett
priority: normal
severity: normal
status: open
title: regex module fails with a quantified backref but succeeds with repeated
backref
type: behavior
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43726>
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