[Distutils] PEP 426 (Metadata 2.0) - Requires-Dist and setuptools/distribute

Nick Coghlan ncoghlan at gmail.com
Tue Mar 5 23:39:09 CET 2013

On 6 Mar 2013 00:59, "PJ Eby" <pje at telecommunity.com> wrote:
> On Mon, Mar 4, 2013 at 3:20 PM, Paul Moore <p.f.moore at gmail.com> wrote:
> > On 4 March 2013 20:00, Daniel Holth <dholth at gmail.com> wrote:
> >> On Mon, Mar 4, 2013 at 2:41 PM, Paul Moore <p.f.moore at gmail.com> wrote:
> >>> In thinking about how virtualenv would describe the packages it wants
> >>> to preload in PEP 426 metadata form, it occurred to me that there are
> >>> scenarios with setuptools and distribute where it's not obvious how to
> >>> state the requirement you want. Specifically, if you want to install
> >>> setuptools if it is present, but if not fall back to distribute (for
> >>> example, if you have a local package repository and no access to PyPI,
> >>> but setuptools may or may not be present).
> > [...]
> >>
> >> We do have Provides-Dist, although the best way to implement it is an
> >> open question.
> >
> > Good point. So distribute would have "Provides-Dist: setuptools" and I
> > could just require setuptools. Given that none of this is supported
> > yet, I'm happy that the spec covers this case, but still need to work
> > around it for the immediate future.
> Provides-Dist doesn't actually work for most of the use cases for
> alternates, though.  For example, if a package that wants to require
> one of the various mysql adapters, it doesn't make any sense for the
> mysql packages to declare that they provide each other.  ;-)

The adapter developers just need to agree on a virtual provides they will
all publish. Of course, that won't be effective without an entry points
extension to get the adapters loaded in a consistent fashion.

Still, one step at a time :)


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