[Distutils] something else to throw into the static metadata mix

[Thomas Lotze]

Chris Withers wrote:

> I think you're missing my point: how would the package be named and/or how
> would you express in static metadata, that a particular version of the
> package is for postgres 8 rather than postgres 7, or 8.4 rather than 8.3?

Just to add my 2 cents: It seems to me that there are two sets of metadata
getting confused here. One is the existing set including the Python
dependencies. This set is meant to describe what the package does and
relies on conceptually. The other is a set of system dependencies that
describe in what precise environment a binary egg happens to have been
built.

The latter are currently expressed only in the file name of the egg or not
at all. The set of system dependencies can be taken to be empty for a
source egg and includes the target platform and architecture, some of the
options Python was built with (what flavour of unicode, which optional
libraries compiled in), and a set of third-party system libraries with or
without version restrictions.

Of the system dependencies, only the platform and architecture are
currently accessible (through the egg file name) when downloading an egg,
which is one of the reasons why releasing binary eggs for Linux is so
unpopular - you might just end up with an unforeseeable mismatch of
unicode flavour between your Python and the binary egg.

In a dream world, a package index would have an API that allows an
installer to query what system dependencies are relevant to binary eggs of
a given package and for which combinations of values binary eggs actually
exist. The installer could then figure out which of them fits its actual
environment best or whether to get the source egg and roll its own binary.

-- 
Thomas