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Groups > comp.lang.python > #48644

Re: Why is regex so slow?

Subject Re: Why is regex so slow?
From Roy Smith <roy@panix.com>
Date 2013-06-18 13:08 -0400
References <kpq2r9$gg6$1@panix2.panix.com> <CANc-5UyouN5EQw_GDecaAR+inyAB26g=e2pZ=zBuspXdmxJh+Q@mail.gmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.3544.1371575342.3114.python-list@python.org> (permalink)

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On Jun 18, 2013, at 1:01 PM, Skip Montanaro wrote:

>> I don't understand why the first way is so much slower.
> 
> I have no obvious answers, but a couple suggestions:
> 
> 1. Can you anchor the pattern at the beginning of the line?  (use
> match() instead of search())

That's one of the things we tried.  Didn't make any difference.

> 2. Does it get faster it you eliminate the "(.*)" part of the pattern?

Just tried that, it also didn't make any difference.

> It seems that if you find a line matching the first part of the
> pattern, you could just as easily split the line yourself instead of
> creating a group.


At this point, I'm not so much interested in making this faster as understanding why it's so slow.  I'm tempted to open this up as a performance bug against the regex module (which I assume will be rejected, at least for the 2.x series).

---
Roy Smith
roy@panix.com

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Thread

Why is regex so slow? roy@panix.com (Roy Smith) - 2013-06-18 12:45 -0400
  Re: Why is regex so slow? Skip Montanaro <skip@pobox.com> - 2013-06-18 12:01 -0500
  Re: Why is regex so slow? Roy Smith <roy@panix.com> - 2013-06-18 13:08 -0400
  Re: Why is regex so slow? Chris Angelico <rosuav@gmail.com> - 2013-06-19 03:20 +1000
    Re: Why is regex so slow? Johannes Bauer <dfnsonfsduifb@gmx.de> - 2013-06-18 20:10 +0200
      Re: Why is regex so slow? Roy Smith <roy@panix.com> - 2013-06-18 12:40 -0700
      Re: Why is regex so slow? André Malo <ndparker@gmail.com> - 2013-06-18 21:59 +0200
        Re: Why is regex so slow? André Malo <ndparker@gmail.com> - 2013-06-18 22:13 +0200
  Re: Why is regex so slow? MRAB <python@mrabarnett.plus.com> - 2013-06-18 18:31 +0100
  Re: Why is regex so slow? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-06-18 18:34 +0100
    Re: Why is regex so slow? roy@panix.com (Roy Smith) - 2013-06-18 15:21 -0400
      Re: Why is regex so slow? MRAB <python@mrabarnett.plus.com> - 2013-06-18 20:49 +0100
  Re: Why is regex so slow? Rick Johnson <rantingrickjohnson@gmail.com> - 2013-06-18 12:21 -0700
  Re: Why is regex so slow? Antoine Pitrou <solipsis@pitrou.net> - 2013-06-18 20:05 +0000
    Re: Why is regex so slow? Roy Smith <roy@panix.com> - 2013-06-18 13:23 -0700
      Re: Why is regex so slow? Duncan Booth <duncan.booth@invalid.invalid> - 2013-06-19 13:21 +0000
        Re: Why is regex so slow? Roy Smith <roy@panix.com> - 2013-06-19 12:55 -0700
    Re: Why is regex so slow? Grant Edwards <invalid@invalid.invalid> - 2013-06-18 20:30 +0000
      Re: Why is regex so slow? Terry Reedy <tjreedy@udel.edu> - 2013-06-18 17:29 -0400
      Re: Why is regex so slow? Johannes Bauer <dfnsonfsduifb@gmx.de> - 2013-06-19 10:29 +0200
  Re: Why is regex so slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-19 01:51 +0000
    Re: Why is regex so slow? Dave Angel <davea@davea.name> - 2013-06-18 22:11 -0400
      Re: Why is regex so slow? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-06-19 03:16 +0000

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