[Python-Dev] cpython: Use cached builtins.

[Michael Foord]

On 3 Oct 2013, at 12:05, Nick Coghlan <ncoghlan at gmail.com> wrote:

> 
> On 3 Oct 2013 06:00, "Victor Stinner" <victor.stinner at gmail.com> wrote:
> >
> > I don't remember where, but I remember that I also saw things like
> > "str=str, len=len, ...". So you keep the same name, but you use fast
> > local lookups instead of slow builtin lookups.
> 
> functools uses the local binding trick in lru_cache as a speed hack (pretty sure it uses an underscore prefix, though).
> 


Inside a function you *have* to use an underscore prefix (well, some alternate name anyway) - otherwise the assignment makes the name local and the lookup would fail with an unbound local error. In order to do the binding at definition time rather than call time (so only once) the assignment is often done in the function signature. This is *particularly* ugly as it not only messes up the using of the builtins but screws your function signature too. So It should really only be done where benchmarking proves it makes a difference. I've never managed to find such a case...

Michael

> However lru_cache *is* likely to end up being speed critical *and* it's binding local variables , so it's actually shifting a lot more work to compile time than merely trading a builtin lookup for a global lookup does.
> 
> For most code though, introducing that kind of complexity isn't worth the cost in readability.
> 
> Cheers,
> Nick.
> 
> >
> > Victor
> >
> > 2013/10/2 Antoine Pitrou <solipsis at pitrou.net>:
> > > On Wed,  2 Oct 2013 18:16:48 +0200 (CEST)
> > > serhiy.storchaka <python-checkins at python.org> wrote:
> > >> http://hg.python.org/cpython/rev/d48ac94e365f
> > >> changeset:   85931:d48ac94e365f
> > >> user:        Serhiy Storchaka <storchaka at gmail.com>
> > >> date:        Wed Oct 02 19:15:54 2013 +0300
> > >> summary:
> > >>   Use cached builtins.
> > >
> > > What's the point? I don't think it's a good idea to uglify the code if
> > > there isn't a clear benefit.
> > >
> > > Regards
> > >
> > > Antoine.
> > >
> > >
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