[Python-Dev] advice needed: best approach to enabling "metamodules"?

[Guido van Rossum]

On Sun, Nov 30, 2014 at 1:12 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Sun, 30 Nov 2014 11:15:50 -0800
> Guido van Rossum <guido at python.org> wrote:
> > On Sun, Nov 30, 2014 at 6:15 AM, Brett Cannon <brett at python.org> wrote:
> > >
> > >  On Sat, Nov 29, 2014, 21:55 Guido van Rossum <guido at python.org>
> wrote:
> > >
> > > All the use cases seem to be about adding some kind of getattr hook to
> > > modules. They all seem to involve modifying the CPython C code anyway.
> So
> > > why not tackle that problem head-on and modify module_getattro() to
> look
> > > for a global named __getattr__ and if it exists, call that instead of
> > > raising AttributeError?
> > >
> > >  Not sure if anyone thought of it. :) Seems like a reasonable solution
> to
> > > me. Be curious to know what the benchmark suite said the impact was.
> > >
> > Why would there be any impact? The __getattr__ hook would be similar to
> the
> > one on classes -- it's only invoked at the point where otherwise
> > AttributeError would be raised.
>
> builtins are typically found by first looking up in the current globals
> (module) scope, failing, and then falling back on __builtins__.
>
> Depending on how much overhead is added to the "failing" step, there
> /might/ be a performance difference. Of course, that would only occur
> wherever a __getattr__ hook is defined.
>

The builtins lookup process never does a module attribute lookup -- it only
does dict lookups. So it would not be affected by a module __getattr__ hook
(unless we were to use dict proxies, which Nathaniel already rejected).

@Nathaniel: perhaps you could get what you want without any C code changes
using the approach of Brett's LazyLoader?

-- 
--Guido van Rossum (python.org/~guido)
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