[Distutils] nspkg.pth files break $PYTHONPATH overrides

[PJ Eby]

On Tue, Mar 25, 2014 at 3:50 PM, Barry Warsaw <barry at python.org> wrote:

> On Mar 25, 2014, at 03:35 PM, PJ Eby wrote:
>
> >I think the correct fix would be to change the nspkg.pth magic to check
> for
> >PEP 420 support, but unfortunately it seems we may have to use version
> >checking: on rereading PEP 420 I see there's no 'sys.namespace_packages'
> or
> >similar object that can be directly checked for feature support.  :-(
>
> There is.  It's *pronounced* sys.namespace_packages, but it's spelled
> importlib._bootstrap._NamespaceLoader ;)
>

Yeah, well that's not exactly a public attribute, so it's not necessarily a
great way to do it.  But if we did use that, presumably it'd add something
like:

    hnp =
hasattr(sys.modules.get('importlib._bootstrap',None),'_NamespaceLoader');

To the front of the magic, and then prefix all subsequent expression values
with 'not hnp and' in order to prevent them executing if PEP 420 support is
available. (Note: it's checking sys.modules since on any interpreter where
PEP 420 is natively available, the module should *already* be loaded by the
time site.py does its thing.)

And we should probably think about adding sys.namespace_packages or
something of the sort, or at least a proper flag for whether PEP 420
support is available on the platform.
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