[Python-Dev] sre improvements

[Jeff Epler]

On Wed, Jun 13, 2001 at 11:03:58AM -0500, Skip Montanaro wrote:
> 
>     Gustavo> I'd like, for example, to see the (?(1)blah) operator,
>     Gustavo> available in perl, working.
> 
> Gustavo,
> 
> For the non-Perl-heads on the list, can you explain what the (?(1)blah)
> operator does?

from perlre(1):
       (?(condition)yes-pattern)
                 Conditional expression.  (condition) should be
                 either an integer in parentheses (which is valid
                 if the corresponding pair of parentheses
                 matched), or lookahead/lookbehind/evaluate zero-
                 width assertion.

                 Say,

                     m{ ( \( )?
                        [^()]+
                        (?(1) \) )
                      }x

                 matches a chunk of non-parentheses, possibly
                 included in parentheses themselves.

Jeff