[Python-ideas] Fast global cacheless lookup

Guido van Rossum guido at python.org
Thu Nov 22 18:07:58 CET 2007

[Quick] The best way to post a patch is to put it in the bug tracker
at bugs.python.org, and post a link to the issue here. The best way to
create a patch is svn diff, assuming you started out with an anonymous
svn checkout (see python.org/dev/) and not just with a distro

Looking forward to it!


On Nov 22, 2007 8:42 AM, Neil Toronto <ntoronto at cs.byu.edu> wrote:
> Guido van Rossum wrote:
> > Cool! Are you willing to show the code yet (bugs and all)?
> Sure! I stayed up all night doing it and today is Thanksgiving, so I'll
> probably not get to it for a little while. (I know making a patch
> shouldn't take long, but I've never done it before.) Should I post the
> patch here or somewhere else?
> > Some questions:
> >
> > - what's the space & time impact for a dict with no watchers?
> I think it's almost negligible.
> Space: There are four bytes extra on every dict for a pointer to the
> observer list. It may actually be zero or eight or more depending on
> alignment and malloc block size - I haven't looked.
> Time: On dicts with no observers, dealloc, delitem, pop, popitem, clear,
> and resize pass through an "if (mp->ma_entryobs_list != NULL)".
> PyDict_New sets mp->ma_entryobs_list to NULL. Nothing else is affected.
> > - does this do anything for builtins?
> It does right now well enough to get them quickly, but setting or
> deleting them elsewhere won't show up yet in the frame. And it doesn't
> handle the case where __builtins__ is replaced. That'll take a little
> doing, but just mentally - it shouldn't affect performance much.
> Anyway, that part will work properly when I'm done.
> > - could this be made to work for instance variables?
> If my brain were thinking in straight lines, maybe I'd come up with
> something. :) I've got this fuzzy idea that it just might work. The hard
> part may be distinguishing LOAD_ATTR applied to self from LOAD_ATTR
> applied to something else. Hmm...
> Something to digest while I'm digesting the Real Other White Meat. :)
> > - what about exec(src, ns) where ns is a mapping but not a dict?
> Good question - I don't know, but I think it should work, at least as
> well as it did before. If there's no observer attached to a frame, it'll
> default to its previous behavior. Another hmm...
> Thanks for the prompt reply.
> Neil
> P.S. By the way, I'm very pleased with how clean and workable the
> codebase is. I actually cheered at the lack of warnings. My wife
> probably thinks I'm nuts. :D
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--Guido van Rossum (home page: http://www.python.org/~guido/)

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