Re: [gentoo-python] Reducing exceptionality cases for PYTHON_SINGLE_TARGET

[Ian Stakenvicius <axs@gentoo.org>]

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On 29/10/14 02:25 PM, W. Trevor King wrote:
> On Wed, Oct 29, 2014 at 02:17:29PM -0400, Ian Stakenvicius wrote:
>> As python-single-r1.eclass is meant to ensure that a package is 
>> bound to just one implementation when multiple implementations 
>> are possible, usually because it is too difficult to make the 
>> package multibuild, it would make sense to me that if there is 
>> actually just one possible implementation…
> 
> I understand “It's too difficult for me to get this build system to
> work with multiple Python versions.”  I'm skeptical that there are
> any packages where “there is actually just one possible 
> implementation.” Still I agree that some users will want a way to 
> say “if I ask for a package that only installs for one Python 
> implementation, just install it without my needing to tweak my USE 
> flags.”

There's a ton of packages that are only python2 -- that is, have
PYTHON_COMPAT=( python2_{6,7} ) or equivalent, and since python2_6
(and earlier) isn't in the supported implementations list, that leaves
just python2_7.  If you'd like, I can do up a list.

> Personally, I'd prefer to stick with my existing 
> PYTHON_SINGLE_TARGET. If a package doesn't like that, I can think 
> harder about whether or not I actually need the package.  My
> Docker images [1], for example, are single-Python implementations
> and I don't want to pull in another Python accidentally.

This change will not pull in extra python versions, it just changes
the python-single-r1 inheriting ebuilds so that they rely on the
values set in PYTHON_TARGETS for resolution, instead of
PYTHON_SINGLE_TARGET.

So the only way you would accidentally pull in a different python is
if you didn't set PYTHON_TARGETS, or set it to have multiple values.
PYTHON_SINGLE_TARGET is only for choosing which of the PYTHON_TARGETS
values should be used when a package can't multibuild.


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