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

[Guido van Rossum]

On Sun, Nov 30, 2014 at 5:42 PM, Nathaniel Smith <njs at pobox.com> wrote:

> On Mon, Dec 1, 2014 at 1:27 AM, Guido van Rossum <guido at python.org> wrote:
> > Nathaniel, did you look at Brett's LazyLoader? It overcomes the subclass
> > issue by using a module loader that makes all modules instances of a
> > (trivial) Module subclass. I'm sure this approach can be backported as
> far
> > as you need to go.
>
> The problem is that by the time your package's code starts running,
> it's too late to install such a loader. Brett's strategy works well
> for lazy-loading submodules (e.g., making it so 'import numpy' makes
> 'numpy.testing' available, but without the speed hit of importing it
> immediately), but it doesn't help if you want to actually hook
> attribute access on your top-level package (e.g., making 'numpy.foo'
> trigger a DeprecationWarning -- we have a lot of stupid exported
> constants that we can never get rid of because our rules say that we
> have to deprecate things before removing them).
>
> Or maybe you're suggesting that we define a trivial heap-allocated
> subclass of PyModule_Type and use that everywhere, as a
> quick-and-dirty way to enable __class__ assignment? (E.g., return it
> from PyModule_New?) I considered this before but hesitated b/c it
> could potentially break backwards compatibility -- e.g. if code A
> creates a PyModule_Type object directly without going through
> PyModule_New, and then code B checks whether the resulting object is a
> module by doing isinstance(x, type(sys)), this will break. (type(sys)
> is a pretty common way to get a handle to ModuleType -- in fact both
> types.py and importlib use it.) So in my mind I sorta lumped it in
> with my Option 2, "minor compatibility break". OTOH maybe anyone who
> creates a module object without going through PyModule_New deserves
> whatever they get.
>

Couldn't you install a package loader using some install-time hook?

Anyway, I still think that the issues with heap types can be overcome. Hm,
didn't you bring that up before here? Was the conclusion that it's
impossible?

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