[Python-Dev] Fwd: PEP 426 is now the draft spec for distribution metadata 2.0 (original) (raw)

PJ Eby pje at telecommunity.com
Thu Feb 21 00:36:21 CET 2013

On Wed, Feb 20, 2013 at 5:30 AM, M.-A. Lemburg <mal at egenix.com> wrote:

The wording in the PEP alienates the egg format by defining an incompatible new standard for the location of the metadata file:

This isn't a problem, because there's not really a use case at the moment for eggs to include a PEP 426-format metadata file, and if they ever do, it ought to be called METADATA, so that pkg_resources will know to read it if there are no egg-format dependencies listed. Setuptools also doesn't care what format PKG-INFO is in, as it only ever reads the "Version:" field, and that only in the case of in-development source packages.

It's easy to upgrade distribute and distutils to write metadata 1.2 format, simply by changing the version in the PKG-INFO files.

As soon as distutils does it, setuptools will do it, because setuptools delegates metadata writing to distutils. So there's no "alienation" here.

What will need to happen at some point is for pkg_resources to implement support for PEP 426-style version requirements, which I haven't tried to fully wrap my head around as yet. I'm hoping that there are simple textual substitutions (e.g. regexes) that can be done to convert them to pkg_resources requirements. If need be, I'll swipe whatever's needed from distlib. ;-)

In the meantime, eggs aren't actually going anywhere, since wheels aren't actually trying to replace all of their use cases. And since the new metadata and binary formats don't actually add much new functionality over what eggs already do, eggs wouldn't lose much by not being able to use the same metadata, anyway. ;-)

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