[Distutils] warning about potential problem for wheels

[Oscar Benjamin]

On Sat, 10 Oct 2015 20:53 Laura Creighton <lac at openend.se> wrote:

(note, I currently don't have mail delivery on for distutils.  I could
change this, but right now I don't think I have a lot to contribute.
This is just a warning).

If you have old windows hardware, which does not support SSE2, and
windows 7, you can build your own python 3.5.  This will work. But
wheels won't, you will need to build them from source as well.
see: http:// <http://bugs.python.org/issue25361>bugs.python.org
<http://bugs.python.org/issue25361>/issue25361
<http://bugs.python.org/issue25361>

This means that wheels could start failing.  It would be good if
the wheels themselves could detect this problem and protest in a
reasonable fashion, but I have no idea if this is possible.  In any
case, I thought you needed to know.



There is no way for wheels to do this. A wheel is just a zip file with a
standardised layout. Pip just extracts the zip, reads the metadata and
copies the files to the appropriate locations. The metadata has no way to
describe the fact that it the wheel contains SSE2 dependent binaries. The
standard tools used to create wheels don't know anything about the contents
of the compiled binaries so they don't really have a way to detect that the
wheel depends on SSE2.

Really this is just a case of an unsupported platform. It's unfortunate
that CPython doesn't properly support this hardware but I think it's
reasonable that if you have to build your interpreter from source then you
have to build your extension modules as well.

I'm not sure of a robust solution to detecting the problem at install time.
Extension module authors can only really guarantee that their Windows
binaries are compatible with standard released binaries. So if someone
builds their own interpreter using different compiler options then there's
no real way for pip or the extension module author to know if the binaries
will be compatible. So either pip rejects all binaries for a non standard
interpreter build or it installs them and hopes for the best.

--
Oscar
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