[issue9179] Lookback with group references incorrect (two issues?)

[Matthew Barnett]

Matthew Barnett <python at mrabarnett.plus.com> added the comment:

Should a regex compile if a group is referenced before it's defined?

Consider this:

    (?:(?(2)(a)|(b))+

Other regex implementations permit forward references to groups.

BTW, I had a look at the re module, found it too difficult, and so started on my own implementation of the matching engine (available on PyPI).

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<http://bugs.python.org/issue9179>
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