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Re: Why is regex so slow?

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On 18/06/2013 20:21, Roy Smith wrote:
> In article <mailman.3549.1371576854.3114.python-list@python.org>,
> Mark Lawrence  <breamoreboy@yahoo.co.uk> wrote:
>
>> Out of curiousity have the tried the new regex module from pypi rather
>> than the stdlib version?  A heck of a lot of work has gone into it see
>> http://bugs.python.org/issue2636
>
> I just installed that and gave it a shot.  It's *slower* (and, much
> higher variation from run to run).  I'm too exhausted fighting with
> OpenOffice to get this into some sane spreadsheet format, so here's
> the raw timings:
>
> Built-in re module:
> 0:01.32
> 0:01.33
> 0:01.32
> 0:01.33
> 0:01.35
> 0:01.32
> 0:01.35
> 0:01.36
> 0:01.33
> 0:01.32
>
> regex with flags=V0:
> 0:01.66
> 0:01.53
> 0:01.51
> 0:01.47
> 0:01.81
> 0:01.58
> 0:01.78
> 0:01.57
> 0:01.64
> 0:01.60
>
> regex with flags=V1:
> 0:01.53
> 0:01.57
> 0:01.65
> 0:01.61
> 0:01.83
> 0:01.82
> 0:01.59
> 0:01.60
> 0:01.55
> 0:01.82
>
I reckon that about 1/3 of that time is spent in 
PyArg_ParseTupleAndKeywords, just getting the arguments!

There's a higher initial overhead in using regex than string methods,
so working just a line at time will take longer.

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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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