Variable-width lookbehind

[OKB (not okblacke)]

Gary Herron wrote:

> OKB (not okblacke) wrote:
>> Paul Rubin wrote:
>>
>>   
>>> "OKB (not okblacke)" <brenNOSPAMbarn at NObrenSPAMbarn.net> writes:
>>>     
>>>>          For years now Python has not supported variable-length
>>>>          lookbehinds.  
>>>>       
>>> I'm not sure what that is and the perl links you gave don't work,
>>> but it sounds evil. 
>>>     
>>
>>          The links work fine for me. . .
>>
>>          You're not sure what "variable-length lookbehinds" means?
>>           
>> Lookbehind is something that Python regexps already have.  You can
>> do "(?<=one)two" to match "two" only if it's preceded by "one",
>> and you can do "(?<!one)two" to match "two" only if it's NOT
>> preceded by "one".  What you can't do is "(?<=one|three)two",
>> because Python requires that the lookbehind contain only strings
>> of a fixed length.  What I'm asking about is the possibility of
>> lifting this limitation, to allow the lookbehinds (positive and
>> negative) to contain general regexps.  I don't see how this is in
>> any way evil. 
>>   
> If not *evil*, then how about *unreadable*.   Regular expressions
> are powerful, but nearly unreadable as they are.  Allowing them to
> be even more complex just gets one step closer to *absolutely
> unreadable*. 

    	Well, it doesn't really change the potential for unreadability.  It 
just allows people to put existing unreadable (or readable) regexps 
inside a particular kind of group.

> Are you willing to implement it and lobby for it's inclusion?  If
> so, good, we'll look at it.  If not, then perhaps you understand
> perfectly why it's not yet included.

    	Yeah, this is what I was expecting, and it's a valid point.  I was 
just wondering if this had ever been floated before.  I personally have 
nowhere near the chops to write something like a regex engine (that's 
why I like using Python -- it's got one built in!).

-- 
--OKB (not okblacke)
Brendan Barnwell
"Do not follow where the path may lead.  Go, instead, where there is
no path, and leave a trail."
	--author unknown