Variable-width lookbehind

OKB (not okblacke) brenNOSPAMbarn at
Tue Nov 20 08:22:46 CET 2007

Tim Roberts wrote:

> "OKB (not okblacke)" <brenNOSPAMbarn at> wrote:
>>         For years now Python has not supported variable-length
>>         lookbehinds.  
>>I'm just curious whether there are any plans to change this in
>>Python 3.0, or before, or after.  It seems that Perl 6 will allow
>>variable- width lookbehinds (see
>> and
>> ). 
> If I may be just a bit catty, your last sentence may actually be
> the best reason NOT to include it in Python 3.0.  Perl 6 has become
> a worthy successor to ALGOL 68 and PL/I.  They are attempting to
> pack in every feature that has ever been requested by every person
> in the known universe. 

    	That's as may be, but if I may be a bit redundant with myself, I'd 
like to reiterate that I don't see this is as a new "feature".  Regular 
expressions already exist in Python.  Lookbehinds already exist in 
Python regular expressions.  The only thing that doesn't exist is the 
ability to use arbitrary regular expressions in lookbehinds, and my 
understanding is that this is just because regular expression engines 
have typically been implemented in a way that makes this hard to add on.  
In other words, what I'm describing isn't an extension of what regular 
expressions are, it's just the lifting of a bothersome implementation-
based restriction on one aspect of their use.

--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

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