[Numpy-discussion] [SciPy-dev] Announcing toydist, improving distribution and packaging situation

[David Cournapeau]

On Sat, Jan 2, 2010 at 4:58 PM, Gael Varoquaux
<gael.varoquaux at normalesup.org> wrote:
> On Sat, Jan 02, 2010 at 11:32:00AM +0900, David Cournapeau wrote:
>> [snip]
>>   - supporting different variants of the same package in the
>> dependency graph at install time
>
>> [snip]
>
>> The second issue is more challenging. It complicates the dependency
>> handling quite a bit, and may cause difficult situations to happen at
>> dependency resolution time. This becomes particularly messy if you mix
>> packages you build yourself with packages grabbed from a repository. I
>> wonder if there is a simpler solution which would give a similar
>> feature set.
>
>
> AFAICT, in Debian, the same feature is given via virtual packages: you
> would have:

I don't think virtual-packages entirely fix the issue. AFAIK, virtual
packages have two uses:
 - handle dependencies where several packages may resolve one
particular dependency in an equivalent way (one good example is
LAPACK: both liblapack and libatlas provides the lapack feature)
 - closer to this discussion, you can build several variants of the
same package, and each variant would resolve the dependency on a
virtual package handling the commonalities. For example, say we have
two numpy packages, one built with lapack (python-numpy-full), the
other without (python-numpy-core). What happens when a package foo
depends on numpy-full, but numpy-core is installed ? AFAICS, this can
only work as long as the set containing every variant can be ordered
(in the conventional set ordering sense), and the dependency can be
satisfied by the smallest one.

cheers,

David