Optimizing multiple dispatch

Jeff Epler jepler at unpythonic.net
Thu Jun 3 17:30:40 CEST 2004


Pyrex is just a translator, there's no dependency on a Pyrex library or
include file when you actually want to compile the generated .c

On Thu, Jun 03, 2004 at 04:55:19PM +0200, Jacek Generowicz wrote:
> Jeff Epler <jepler at unpythonic.net> writes:
> 
> > Avoding map() may help:
> >     tuple([type(a) for a in args])
> 
> Nonononononooooo!  :-)
[...]
> > ... hmm, map is faster than listcomp.  my mistake!
> 
> :-)
> 
> I've asked for optimization advice a few times here, and usually the
> responses include "replace map with a list comprehension" ... and yet
> the map is always faster. I wonder where people get this idea that map
> is slow ... until this started happening I had always assumed that
> "everyone" knows that the map/reduce/filter family are the fastest
> Python looping constructs.

No message about optimization should be without one downright wrong
suggestion.

The common wisdom about listcomp speed may apply when the body doesn't
include a function call, but the map version would include a lambda:
    $ timeit 'map(lambda x:x+1, range(100))'
    1000 loops, best of 3: 230 usec per loop
    $ timeit '[x+1 for x in range(100)]'
    10000 loops, best of 3: 156 usec per loop


Jeff
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