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From: Malte Forkel <malte.forkel@berlin.de>
Subject: Utility to locate errors in regular expressions
Date: Fri, 24 May 2013 14:58:24 +0200
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Xref: csiph.com comp.lang.python:45881

Finding out why a regular expression does not match a given string can
very tedious. I would like to write a utility that identifies the
sub-expression causing the non-match. My idea is to use a parser to
create a tree representing the complete regular expression. Then I could
simplify the expression by dropping sub-expressions one by one from
right to left and from bottom to top until the remaining regex matches.
The last sub-expression dropped should be (part of) the problem.

As a first step, I am looking for a parser for Python regular
expressions, or a Python regex grammar to create a parser from.

But may be my idea is flawed? Or a similar (or better) tools already
exists? Any advice will be highly appreciated!

Malte