I need some help with a regexp please

[Frederic Rentsch]

Dennis Lee Bieber wrote:
> On 25 Sep 2006 10:25:01 -0700, "codefire" <tony.bedford at gmail.com>
> declaimed the following in comp.lang.python:
>
>   
>> Yes, I didn't make it clear in my original post - the purpose of the
>> code was to learn something about regexps (I only started coding Python
>> last week). In terms of learning "a little more" the example was
>> successful. However, creating a full email validator is way beyond me -
>> the rules are far too complex!! :)
>>     
>
> 	I've been doing small things in Python for over a decade now
> (starting with the Amiga port)...
>
> 	I still don't touch regular expressions... They may be fast, but to
> me they are just as much line noise as PERL... I can usually code a
> partial "parser" faster than try to figure out an RE.
>   
If I may add another thought along the same line: regular expressions 
seem to tend towards an art form, or an intellectual game. Many 
discussions revolving around regular expressions convey the impression 
that the challenge being pursued is finding a magic formula much more 
than solving a problem. In addition there seems to exist some code of 
honor which dictates that the magic formula must consist of one single 
expression that does it all. I suspect that the complexity of one single 
expression grows somehow exponentially with the number of 
functionalities it has to perform and at some point enters a gray zone 
of impending conceptual intractability where the quest for the magic 
formula becomes particularly fascinating. I also suspect that some 
problems are impossible to solve with a single expression and that no 
test of intractability exists other than giving up after so many hours 
of trying.
    With reference to the OP's question, what speaks against passing his 
texts through several simple expressions in succession? Speed of 
execution? Hardly. The speed penalty would not be perceptible. 
Conversely, in favor of multiple expressions speaks that they can be 
kept simple and that the performance of the entire set can be 
incrementally improved by adding another simple expression whenever an 
unexpected contingency occurs, as they may occur at any time with 
informal systems. One may not win a coding contest this way, but saving 
time isn't bad either, or is even better.

Frederic