[Distutils] OS X and PEP 425 / wheels

[Ned Deily]

In article 
<CAHNn8BW+UfQRFqsuszq81WHM+xthEb-RP-D9Na0TktTgjPHCyw at mail.gmail.com>,
 MinRK <benjaminrk at gmail.com> wrote:
> I proposed a patch <https://github.com/pypa/pip/pull/1465> to pip, with
> respect to treatment of the platform tag on OS X, and Chris Barker proposed
> that I bring the discussion here.
> 
> The situation:
> 
> PEP 425 describes the platform tag as:
> 
> The platform tag is simply distutils.util.get*platform() with all hyphens -
> and periods . replaced with underscore *.
> 
> but the PEP makes no mention of what should be done on OS X. On OS X,
> get_platform() has the form:
> 
> macosx_10_6_intel
> 
> where 10_6 indicates that the OS X deployment target (of Python) is 10.6,
> and intel indicates that it is a fat binary with both x86_64 and i386.
> Other values for the arch include 'ppc', 'ppc64', and 'universal', another
> multi-arch tag indicating a fat binary with all four of 32/64bit intel and
> ppc.

As I commented in your pull request, the complete set of universal arch 
values is "fat", "intel", "fat3", "fat64", and "universal" besides the 
single arch values "ppc", "ppc64", "i386", and "x86_64".  It would be 
best if all of them were supported in pip.

> Where PEP 425 causes problems (or pip's implementation thereof), is in
> testing strict equality of this value, not taking into account the meaning
> of its contents. I proposed two changes:
> 
>    1.
> 
>    Use >= comparison for the deployment target
> 
>    From the OS X platform
> documentation<https://developer.apple.com/library/mac/documentation/DeveloperT
> ools/Conceptual/cross_development/Configuring/configuring.html>
>    :
> 
>    Choose a deployment target. This identifies the earliest OS version on
>    which your software can run.
> 
>    so a binary with deployment target = 10.6 should be installable on OS X
>    >= 10.6.
> 
>    This change restores the longstanding behavior of easy_install, where
>    10.6 eggs are installable on >= 10.6.
>     2.
> 
>    support multi-arch names (intel, universal) on their respective
>    components
>     - intel is valid on {x86_64, i386}
>       - universal is valid on {intel, x86_64, i386, ppc64, ppc}
> 
>    easy_install, like pip, also does strict comparison here, so this would
>    be new behavior.
[...]
> With both proposed changes, I could communicate the same information with
> just one tag:
> 
> pyzmq-14.1.0-cp27-none-macosx_10_6_intel.whl
>
> Any feedback from experts, especially if my understanding of deployment
> targets or fat binaries is incorrect, would be much appreciated.

Thanks for actually proposing an implementation of this.  I think both 
changes should be implemented, with the proviso that all universal arch 
values are supported (for example, the "fat" universal arch is still 
used in current 32-bit-only python.org Pythons.  As I also noted in the 
comments, it is not a perfect solution since it doesn't cover all 
possible cases (like Unicode ABI).  That will have to wait for Metadata 
2.0.  But it does provide important usability gains for OS X users right 
now and covers the most common (by far) use cases.

-- 
 Ned Deily,
 nad at acm.org