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To: python-list@python.org
From: rh <richard_hubbe11@lavabit.com>
Subject: Re: Curious to see alternate approach on a search/replace via regex
Date: Wed, 6 Feb 2013 19:31:08 -0800
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On 07 Feb 2013 03:04:39 GMT
Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:

> On Wed, 06 Feb 2013 13:55:58 -0800, Demian Brecht wrote:
> 
> > Well, an alternative /could/ be:
> > 
> > from urlparse import urlparse
> > 
> > parts =
> > urlparse('http://alongnameofasite1234567.com/q?sports=run&a=1&b=1')
> > print '%s%s_%s' % (parts.netloc.replace('.', '_'),
> >     parts.path.replace('/', '_'),
> >     parts.query.replace('&', '_').replace('=', '_') )
> > 
> > 
> > Although with the result of:
> > 
> > alongnameofasite1234567_com_q_sports_run_a_1_b_1
> >          1288 function calls in 0.004 seconds
> > 
> > 
> > Compared to regex method:
> > 
> > 498 function calls (480 primitive calls) in 0.000 seconds
> > 
> > I'd prefer the regex method myself.
> 
> I dispute those results. I think you are mostly measuring the time to 
> print the result, and I/O is quite slow. My tests show that using
> urlparse is 33% faster than using regexes, and far more
> understandable and maintainable.
> 
> 
> py> from urlparse import urlparse
> py> def mangle(url):
> ...     parts = urlparse(url)
> ...     return '%s%s_%s' % (parts.netloc.replace('.', '_'),
> ...             parts.path.replace('/', '_'),
> ...             parts.query.replace('&', '_').replace('=', '_')
> ...             )
> ... 
> py> import re
> py> def u2f(u):
> ...     nx = re.compile(r'https?://(.+)$')
> ...     u = nx.search(u).group(1)
> ...     ux = re.compile(r'([-:./?&=]+)')
> ...     return ux.sub('_', u)
> ... 
> py> s = 'http://alongnameofasite1234567.com/q?sports=run&a=1&b=1'
> py> assert u2f(s) == mangle(s)
> py> 
> py> from timeit import Timer
> py> setup = 'from __main__ import s, u2f, mangle'
> py> t1 = Timer('mangle(s)', setup)
> py> t2 = Timer('u2f(s)', setup)
> py> 
> py> min(t1.repeat(repeat=7))
> 7.2962000370025635
> py> min(t2.repeat(repeat=7))
> 10.981598854064941
> py>
> py> (10.98-7.29)/10.98
> 0.33606557377049184
> 
> 
> (Timings done using Python 2.6 on my laptop -- your speeds may vary.)

I am using 2.7.3 and I put the re.compile outside the function and it
performed faster than urlparse. I don't print out the data. 

Fast
^
|  compiled regex
|  urlparse
|  plain regex
|  all-at-once search/replace with alternation
Slow

> 
> 
> 
> -- 
> Steven