[issue1519638] Unmatched Group issue - workaround

[Gerard]

Gerard <gjp at gp-net.nl> added the comment:

Hi All,

I found a workaround for the re.sub method so it does not raise an
exception but returns and empty string when backref-ing an empty group.

This is the nutshell:

When doing a search and replace with sub, replace the group represented
as optional for a group represented as an alternation with one empty
subexpression. So instead of this “(.+?)?” use this “(|.+?)” (without
the double quotes).

If there’s nothing matched by this group the empty subexpression
matches. Then an empty string is returned instead of a None and the sub
method is executed normally instead of raising the “unmatched group” error.

A complete description is in my post:
http://www.gp-net.nl/2008/07/11/solved-python-regex-raising-exception-unmatched-group/


Regards,

Gerard.

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nosy: +gerardjp
title: Unmatched Group issue -> Unmatched Group issue - workaround

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue1519638>
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