[Python-Dev] New regex module for 3.2?

Georg Brandl g.brandl at gmx.net
Thu Jul 22 13:34:35 CEST 2010

Am 13.07.2010 15:35, schrieb Antoine Pitrou:
> On Tue, 13 Jul 2010 15:20:23 +0100
> Michael Foord <fuzzyman at voidspace.org.uk> wrote:
>> On 13/07/2010 15:17, Reid Kleckner wrote:
>> > On Mon, Jul 12, 2010 at 2:07 PM, Nick Coghlan<ncoghlan at gmail.com>  wrote:
>> >    
>> >> MRAB's module offers a superset of re's features rather than a subset
>> >> though, so once it has had more of a chance to bake on PyPI it may be
>> >> worth another look.
>> >>      
>> > I feel like the new module is designed to replace the current re
>> > module, and shouldn't need to spend time in PyPI.  A faster regex
>> > library isn't going to motivate users to add external dependencies to
>> > their projects.
>> >
>> >    
>> If the backwards compatibility issues can be addressed and MRAB is 
>> willing to remain as maintainer then the advantages seem well worth it 
>> to me.
> To me as well. The code needs a full review before integrating, though.

FWIW, I've now run the Pygments test suite (Pygments has about 2500 regular
expressions that are exercised there) and only had two problems:

* Scoped flags: A few lexers use (?s) and similar flags at the end of
  the expression, which has no effect in regex currently.

* POSIX character classes: One regex used a class '[][:xyz]', so the [:
  was seen as the start of a character class.  I'm not sure how common
  this is, as most people seem to escape brackets in character classes.
  Also, it gives a clear error on regex.compile(), not "mysterious"

Timings (seconds to run the test suite):

re     26.689  26.015  26.008
regex  26.066  25.797  25.865

So, I thought there wasn't a difference in performance for this use case
(which is compiling a lot of regexes and matching most of them only a
few times in comparison).  However, I found that looking at the regex
caching is very important in this case: re._MAXCACHE is by default set to
100, and regex._MAXCACHE to 1024.  When I set re._MAXCACHE to 1024 before
running the test suite, I get times around 18 (!) seconds for re.


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