Newbie regular expression and whitespace question

[Paul McGuire]

"Fredrik Lundh" <fredrik at pythonware.com> wrote in message
news:mailman.809.1127421945.509.python-list at python.org...
<snip - timing and sample code, comparing pyparsing (test3) with comparable
regexp (test4)>
>
> > timeit -s "import test" "test.test3()"
> 100 loops, best of 3: 6.73 msec per loop
>
> > timeit -s "import test" "test.test4()"
> 10000 loops, best of 3: 27.8 usec per loop
>
> that's a 240x slowdown.  hmm.
>
> </F>
>
>
Well, what of it?  How fast does it have to be?  Is it a one-shot
conversion?  People tend to be willing to wait a bit longer for one-time
conversion programs.  What else is going on in this program?  Is this the
bottleneck?  Are we reading the input over the Internet through HTTP?

If I'm running this program and waiting for the results, 7 msec isn't
perceptibly slower than 28 usec - both are going to seem pretty much
instantaneous.  On the other hand, if I'm processing 100 files, then this
goes up to, um, .7 sec vs 3 msec.

There is no question, regexp's beat the pants off of pyparsing in raw
performance.  But this newsgroup has visited the raw performance issue many
times in the past, usually when responding to the "Python can't be very
fast, it's interpreted" argument.  Raw performance is just one aspect in
determining suitability of a given technical approach.

-- Paul