Re: Regular expression : non capturing groups are faster ?

From	"Octavian Rasnita" <orasnita@gmail.com>
References	<4f02e31c$0$15724$426a74cc@news.free.fr>
Subject	Re: Regular expression : non capturing groups are faster ?
Date	2012-01-03 13:59 +0200
Newsgroups	comp.lang.python
Message-ID	<mailman.4347.1325592105.27778.python-list@python.org> (permalink)

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From: "candide" <candide@free.invalid>
Subject: Regular expression : non capturing groups are faster ?

Excerpt from the Regular Expression HOWTO 
(http://docs.python.org/howto/regex.html#non-capturing-and-named-groups) :

-----------------------------------------------
It should be mentioned that there’s no performance difference in 
searching between capturing and non-capturing groups; neither form is 
any faster than the other.
-----------------------------------------------

Now from the Perl Regular Expression tutorial 
(http://perldoc.perl.org/perlretut.html#Non-capturing-groupings) :

-----------------------------------------------
Because there is no extraction, non-capturing groupings are faster than 
capturing groupings.
-----------------------------------------------

The second assertion sounds more likely. It seems very odd that Python 
and Perl implementations are divergent on this point. Any opinion ?

-- 
**
At least in Perl's case, it is true. I tested and using (?:...) is much faster than ().

Of course, it takes a few seconds for dozen million matches...

Octavian

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Regular expression : non capturing groups are faster ? candide <candide@free.invalid> - 2012-01-03 12:14 +0100
  Re: Regular expression : non capturing groups are faster ? Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-01-03 06:56 -0500
    Re: Regular expression : non capturing groups are faster ? candide <candide@free.invalid> - 2012-01-03 15:50 +0100
      Re: Regular expression : non capturing groups are faster ? Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-01-03 14:31 -0500
      Re: Regular expression : non capturing groups are faster ? "Octavian Rasnita" <orasnita@gmail.com> - 2012-01-03 22:07 +0200
      Re: Regular expression : non capturing groups are faster ? Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-01-03 15:38 -0500
  Re: Regular expression : non capturing groups are faster ? "Octavian Rasnita" <orasnita@gmail.com> - 2012-01-03 13:59 +0200

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