Re: collections.Counter surprisingly slow

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From	Stefan Behnel <stefan_ml@behnel.de>
Subject	Re: collections.Counter surprisingly slow
Date	Mon, 29 Jul 2013 13:46:58 +0200
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Steven D'Aprano, 28.07.2013 22:51:
> Calling Counter ends up calling essentially this code:
> 
> for elem in iterable:
>     self[elem] = self.get(elem, 0) + 1
> 
> (although micro-optimized), where "iterable" is your data (lines). 
> Calling the get method has higher overhead than dict[key], that will also 
> contribute.

It comes with a C accelerator (at least in Py3.4dev), but it seems like
that stumbles a bit over its own feet. The accelerator function special
cases the (exact) dict type, but the Counter class is a subtype of dict and
thus takes the generic path, which makes it benefit a bit less than possible.

Look for _count_elements() in

http://hg.python.org/cpython/file/tip/Modules/_collectionsmodule.c

Nevertheless, even the generic C code path looks fast enough in general. I
think the problem is just that the OP used Python 2.7, which doesn't have
this accelerator function.

Stefan

Thread

collections.Counter surprisingly slow Roy Smith <roy@panix.com> - 2013-07-28 15:59 -0400
  Re: collections.Counter surprisingly slow Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-07-28 20:51 +0000
    Re: collections.Counter surprisingly slow Roy Smith <roy@panix.com> - 2013-07-28 17:57 -0400
    Re: collections.Counter surprisingly slow Stefan Behnel <stefan_ml@behnel.de> - 2013-07-29 13:46 +0200
    Re: collections.Counter surprisingly slow Joshua Landau <joshua@landau.ws> - 2013-07-29 13:07 +0100
  Re: collections.Counter surprisingly slow Serhiy Storchaka <storchaka@gmail.com> - 2013-07-29 09:25 +0300
  Re: collections.Counter surprisingly slow Joshua Landau <joshua@landau.ws> - 2013-07-29 12:49 +0100
  Re: collections.Counter surprisingly slow Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-29 11:19 -0600
  Re: collections.Counter surprisingly slow Serhiy Storchaka <storchaka@gmail.com> - 2013-07-29 22:37 +0300
  Re: collections.Counter surprisingly slow Stefan Behnel <stefan_ml@behnel.de> - 2013-07-30 08:39 +0200
  Re: collections.Counter surprisingly slow Stefan Behnel <stefan_ml@behnel.de> - 2013-07-30 08:51 +0200
  Re: collections.Counter surprisingly slow Serhiy Storchaka <storchaka@gmail.com> - 2013-07-30 16:04 +0300

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