On Tue, Feb 19, 2013 at 9:57 PM, wrote:

...

I've never seen environment markers being used or supported in the wild.

I'm not against modernizing the format, but given that version 1.2 has been out for around 8 years now, without much following, I think we need to make the implementation bit a requirement before accepting the PEP.

PEP 345 has NOT been an approved specification for 8 years. It was first drafted in 2005, but not Accepted until 2010: http://hg.python.org/peps/rev/7d78653a0e79 (as Daniel noted, what became PEP 426 actually started as *another* round of edits to PEP 345) PEP 345 was a first attempt at defining a formal standard that adequately described an *existing* implementation defined software distribution ecosystem built around the behaviour of setuptools. It failed, because it did *not* achieve that goal, and because there were associated declarations along the lines of "to migrate to this standard, you must completely change the way you build and distribute your Python code" (by conflating the setup.py -> setup.cfg migration of distutils2 with the use of the new metadata standard). The response was an overwhelming meh, as people willing migrated to distribute and pip (based on the de facto setuptools standards), while the distutils2 project never made it to production readiness because it was trying to solve too many problems at once. By contrast, the PEP 376 metadata format created at the same time has been adopted quite well. PEPs 345 and 386 were also accepted at a time when python-dev had neither interest nor extensive experience in packaging systems (or if anyone did have such experience, they weren't volunteering that information). So what's changed since 2010 that makes me think the time is right for a new metadata version? 1. We've recognised that without setuptools and/or distribute on board to generate it, and pip to consume it, any new metadata version is dead in the water. That groundwork has been done (mostly by Daniel as part of his work on the wheel format) 2. We've systematically gone through and resolved the significant discrepancies between the formal versioning scheme and the implementation defined behaviour of setuptools and distribute. This means that standards compliant versions will sort the same way in those tools, even if they are not updated. 3. We've addressed other objections PJ Eby (the author of setuptools) had to the previous version of the format (notably the handling of project obsolescence). 4. Various other missing features from setuptools are now supported directly (such as extras) 5. The defined interaction of version specifiers and pre- and post- releases was not useful. The new version fixes that to be something developers are more likely to want (i.e. they won't get pre-releases unless they explicitly reference one). 6. We've enhanced the format so it can handle extensions in a systematic fashion with clearly defined lines of authority based on PyPI distribution names, rather than adding arbitrarily named files to a distribution's info directory without any clear indication of where to find that specification for the file's meaning. 7. I've updated the metadata specification itself, including the addition of the Private-Version field, to more clearly explain to developers that the public Version in their metadata is primarily a tool for communicating the relative ordering of versions to installation tools, but they're still free to use their own preferred version labels internally, and certainly are not obliged to actually use the full complexity of the standard versioning scheme that the installers understand. It's OK if people don't want to read the detailed rationale provided for each of the major changes as part of the PEP, or if they want to dispute a particular piece of that rationale. But merely going "it's too complicated!" or "metadata 1.2 failed, so 2.0 will fail as well!" is not a reasonable response. Software distribution is complicated - trying to oversimplify it is one of the reasons setuptools became necessary. Regards, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia