lp:~pythonregexp2.7/python/issue2636-04
In Perl 5.8, $-style back-references were augmented with the more industry-standard back-slash (reverse solidus) format and more recently in Perl 5.10, the using the \g group and \k keyword construct. As $-style is more or less very old-style Perl-specific, it shall not be implemented in Python. However, the \g-style construct, as well as the \k construct would not only provide a short-hand for keyword argument retrieval but the \g operator also allows for relative back-references. I.e. for an expression like r'(a)\g{-1}', the \g{-1} matches the last match group, which would be 'a' and therefor this expression matches the expression "aa". The main reason for adding the \g operator is to gain this relative back-reference functionality. The \g syntax would also allow for unnamed matches above 99 groups. Back-references could also be added to the standard \number pattern would interfere with the \{ or \- notation. Thus, the new back-reference formats to be added consist of:
\gn - Match group by absolute index n, n >= 1 (cannot be used recursively; n != 0)
\g{n} - Same as \gn to avoid expression ambiguity
\g{-n} - Match group by relative index n, n >= 1; -1 means last, -2 means penultimate read and so forth.
\g{name} - Shorthand for (?P=name)
\k<name> - Shorthand for (?P=name)
(?<name>...) - Shorthand for (?P<name>...)
The Python-specific names will remain in all cases; the Perl-specific extensions will be added in order to bring Python and Perl's regular Expression syntax more in line.
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- 39029. By Jeffrey C. "The TimeHorse" Jacobs <email address hidden>
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- 39028. By Jeffrey C. "The TimeHorse" Jacobs <email address hidden>
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- 39027. By Jeffrey C. "The TimeHorse" Jacobs <email address hidden>
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- 39025. By Jeffrey C. "The TimeHorse" Jacobs <email address hidden>
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