[Distutils] PYD/SO platform tags (#22980)

[Donald Stufft]

> On Dec 12, 2014, at 6:23 PM, Steve Dower <Steve.Dower at microsoft.com> wrote:
> 
> Hi distutils-sig,
> 
> There's a bit of discussion going on at http://bugs.python.org/issue22980 about extending SO tags to include bitness values, and I took the opportunity to look into adding platform tags for .pyd files on Windows.
> 
> There's a patch up there, but I'm interested in any thoughts or concerns people may have that I haven't considered. Distribution is likely to be most affected, and I figured distutils-sig is most likely to have people with strong opinions on the subject anyway, so I'm posting here :)
> 
> Basically, importlib.machinery.EXTENSION_SUFFIXES is all that changes. It'll go from [".pyd"] to [".cp35-win32.pyd", ".cp3-win32.pyd", ".pyd"] (where "win32" may also be "win_amd64", "win_ia64" or "win_arm", which are the platforms that have #ifdefs in pyconfig.h).
> 
> By default, distutils' build_ext will use the first extension, and so builds will get the ".cp35-win32.pyd" tag. You can only get the ".cp3-win32.pyd" tag (for stable ABI) by customizing the build process - I don't think that's an unreasonable expectation, especially on Windows.
> 
> I can see potential for making more generic installable packages with this change, though I'm not pushing for that. The big win is when you're building and testing 32-bit and 64-bit pyds through an IDE - it greatly simplifies how the output directories and search paths are organized.
> 
> Thoughts/concerns?

Well here’s the code that computes what tags pip will accept: https://github.com/pypa/pip/blob/develop/pip/pep425tags.py

Obviously any additional information put into the tag will increase the number of builds someone has to do in order to get full coverage, however if all of the data in that are things that genuinely make things binary incompatible then that’s the right thing to do.

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Donald Stufft
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