On Tue, Feb 19, 2013 at 3:25 PM, Paul Moore <p.f.mo...@gmail.com> wrote:
> On 19 February 2013 13:40, Nick Coghlan <ncogh...@gmail.com> wrote: > >> If a tools wants to support metadata 2.0, it has to support all > >> the complicated stuff as well, i.e. handle the requires fields, > >> the environment markers and version comparisons/sorting. > > > > Which is what distutils2 can be used for now, and what distlib will > > provide without the unwanted build system infrastructure in > > distutils2. > > One particular item in Metadata 2.0 which needs to be addressed is > requirements specifiers, as used in (for example) Requires-Dist. These > take forms like "DistName (>= ver)". There are a number of potential > issues here: > > 1. This differs from the pkg_resources format (which omits the > parentheses). Having 2 subtly different formats is not a good idea in > the long term. At the moment, pkg_resources format is used in pip > requirements (on the command line and in requirement files) as well as > in setuptools/distribute and possibly elsewhere. > 2. There is currently no code that I am aware of that implements this > spec. I don't believe distlib does (yet - give Vinay 5 minutes and who > knows? :-)), pkg_resources as I said implements a different format, > and distutils2, apart from being a big dependency to cover just this > point, only matches the version (not the project name) and presumably > does so using the distutils2 version ordering (which is incompatible > with Metadata 2.0). > 3. The format is fiddly to parse and process - nobody is likely to > implement it for themselves without a library that does it (especially > not when using pkg_resources is so easy). > > The PEP needs a rationale as to why the pkg_resources format wasn't > used, and should suggest a migration path for projects which currently > use the pkg_resources style (such as pip's requirements files). > > Paul We did add full support for Metadata 2.0 Requires-Dist in pkg_resources. The fiddling happens here: https://bitbucket.org/tarek/distribute/src/tip/pkg_resources.py?at=default#cl-2469 The code removes the parenthesis and adds == when no operator was specified to convert us back to the pkg_resources format. The rest of pkg_resources carries on as before. Wheel installs would not pull in dependencies otherwise.
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