[Python-Dev] PEP 396, Module Version Numbers (original) (raw)

Glenn Linderman v+python at g.nevcal.com
Thu Apr 7 06:55:49 CEST 2011

On 4/6/2011 9:08 PM, Nick Coghlan wrote:

On Thu, Apr 7, 2011 at 7:58 AM, Glenn Linderman<v+python at g.nevcal.com> wrote:

Perhaps a different technique would be that if packaging is in use, that it could somehow inject the version from setup.cfg into the module, either by tweaking the source as it gets packaged, or installed, or tweaking the module as/after it gets loaded (the latter still required some runtime dependency on code from the packaging system). A line like the following in some designated-to-"packaging" source file could be replaced during packaging:

version = "7.9.7xxxx" # replaced by "packaging" If you don't upload your module to PyPI, then you can do whatever you want with your versioning info. If you do upload it to PyPI, then part of doing so properly is to package it so that your metadata is where other utilities expect it to be. At that point, you can move the version info over to setup.cfg and add the code into the module to read it from the metadata store.

The PEP doesn't mention PyPI, and at present none of the modules there use "packaging" :) So it wasn't obvious to me that the PEP applies only to PyPI, and I have used modules that were not available from PyPI yet were still distributed and packaged somehow (not using "packaging" clearly).

While there has been much effort (discussion by many) to make "packaging" useful to many, and that is probably a good thing, I still wonder why a packaging system should be loaded into applications when all the code has already been installed. Or is the runtime of "packaging" packaged so that only a small amount of code has to be loaded to obtain "version" and "version"? I don't recall that being discussed on this list, but maybe it has been on more focused lists, sorry for my ignorance... but I also read about embedded people complaining about how many files Python opens at start up, and see no need for a full packaging system to be loaded, just to do version checking.

The guidelines in 396 really only apply to distributed packages, so it doesn't make sense to obfuscate by catering to esoteric use cases. If prviate modules don't work with the standard tools, who is going to care? The module author clearly doesn't, and they aren't distributing it to anyone else. Once they do start distributing it, then their new users will help bring them into line. Having the recommended practice clearly documented just makes it easier for those users to point new module distributors in the right direction.

Oh, I fully agree that there be a PEP with guidelines, and yesterday converted my private versioning system to conform with the names in the PEP, and the style of version string in the referenced PEP. And I distribute my modules -- so far only in a private group, and so far as straight .py files... no use of "packaging". And even if I never use "packaging", it seems like a good thing to conform to this PEP, if I can. Version checking is useful.

(Also, tsk, tsk, Barry for including Standards track proposals in an Informational PEP!)

Cheers, Nick. P.S. A nice coincidental progression: PEP 376, 386 and 396 are all related to versioning and package metadata

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