[Distutils] Python 3.3 / packaging - how to make installation conditional on platform?

[Vinay Sajip]

Éric Araujo <merwok <at> netwok.org> writes:

> This is not a design choice but a bug: http://bugs.python.org/issue11637
> We definitely want to support project-local hooks module, as they will
> certainly be used a lot during the transition years.

Thanks for the pointer. I may need this to be fixed in my pythonv fork, so I
will attempt a patch there.
 
> I’m not sure data files support environment markers.  Anyway, please
> report any info missing from the docs, they’re far from complete.

On further study, I see you're right - environment markers will work only with
some of the data. This gap can certainly be handled by setup hooks, once #11637
is fixed, but there's also another problem which I've encountered: on Windows at
least, installing into the conventional appdata paths is fine for simple
applications, but insufficient for applications that need to interact better
with the Windows ecosystem. For example, if you want to install Powershell
modules, they live not in conventional appdata locations but rather in
subdirectories below a user's Documents folder, which is obtained by making
calls into the Windows Shell API, such as SHGetKnownFolderPath or
SHGetSpecialFolderPath. I can't see any references to these in packaging or
sysconfig, so how are these values being determined? I appreciate that might not
be a packaging issue but rather a sysconfig one, but it's certainly of interest
to packagers :-)

The only references I found to the shell APIs is in PC\bdist_winst\install.c,
which (I presume) wouldn't be invoked during a "pysetup3 install" operation.

So, it seems to me like some way is needed for a project to be able to inject
additional categories like {userdocs} and path mappings for them, for its
resources. I appreciate that this is more an issue for Windows than Unix
platforms, but is there such a mechanism?

Incidentally, I noticed a repeated assignment in
packaging/install.py:_run_install_from_dir():

    func = install_methods[install_method]

is called twice in succession, I couldn't see why.

Regards,

Vinay Sajip