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Fri Nov 15 10:47:56 CET 2013 · https://mail.python.org/pipermail/python-dev/2013-November/130212.html

On 15 November 2013 06:48, Tim Peters <tim.peters at gmail.com> wrote:
> Is that a feature?  Or an accident?  It's very surprising to find a
> non-empty match inside an empty match (the outermost lookahead
> assertion).

Personally, I would read (?=(R))" as finding an empty match at a point
where R starts. There's no implication that R is in any sense "inside"
the match.

(?=(\<\w\w\w\w\w\w)\w\w\w) finds the first 3 characters of words that
are 6 or more characters long. Once again, the lookahead extends
beyond the extent of the main match.

It's obscure and a little bizarre, but I'd say its intended and a
logical consequence of the definitions.

Paul

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[Python-Dev] Finding overlapping matches with re assertions: bug or feature?