[Python-Dev] Zero-width matching in regexes
Terry Reedy
tjreedy at udel.edu
Tue Dec 5 15:26:04 EST 2017
On 12/4/2017 6:21 PM, MRAB wrote:
> I've finally come to a conclusion as to what the "correct" behaviour of
> zero-width matches should be: """always return the first match, but
> never a zero-width match that is joined to a previous zero-width match""".
Is this different from current re or regex?
> If it's about to return a zero-width match that's joined to a previous
> zero-width match, then backtrack and keep on looking for a match.
>
> Example:
>
> >>> print([m.span() for m in re.finditer(r'|.', 'a')])
> [(0, 0), (0, 1), (1, 1)]
>
> re.findall, re.split and re.sub should work accordingly.
>
> If re.finditer finds n matches, then re.split should return a list of
> n+1 strings and re.sub should make n replacements (excepting maxsplit,
> etc.).
--
Terry Jan Reedy
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