Why is regex so slow?

[Mark Lawrence]

On 18/06/2013 18:08, Roy Smith wrote:
>
> 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 at panix.com
>

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

-- 
"Steve is going for the pink ball - and for those of you who are 
watching in black and white, the pink is next to the green." Snooker 
commentator 'Whispering' Ted Lowe.

Mark Lawrence