[New-bugs-announce] [issue34982] re.sub() different behavior in 3.7

[purificant]

New submission from purificant <keilo.at+python.bug.tracker at gmail.com>:

A call to re.sub() returns different results in Python 3.7 compared to versions 3.6 / 3.5 and 2.7

Example behavior in 2.7 / 3.5 and 3.6:
>>> re.sub(r'(([^/]*)(/.*)?)', r'\2.zip/\1/', 'example')
'example.zip/example/'

Example in 3.7.0 and 3.7.1rc2:
>>> re.sub(r'(([^/]*)(/.*)?)', r'\2.zip/\1/', 'example')
'example.zip/example/.zip//'

As you can see the returned string is different for the same regex. re.subn() confirms that 2 replacements are made instead of 1.

Is it intended to have different behaviour in 3.7+ or is this a bug?
Thanks

----------
components: Regular Expressions
messages: 327707
nosy: ezio.melotti, mrabarnett, purificant
priority: normal
severity: normal
status: open
title: re.sub() different behavior in 3.7
versions: Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34982>
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