[Python-Dev] Module version variable

[Michael Foord]

On 16/03/2011 12:53, Barry Warsaw wrote:
> On Mar 16, 2011, at 12:39 PM, Alexander Belopolsky wrote:
>
>> I was editing the turtle module (for issue11571, if you are
>> interested) when I noticed that it has the following line:
>>
>> _ver = "turtle 1.1b- - for Python 3.1   -  4. 5. 2009"
>>
>> This is obviously out of date and this variable is not used anywhere
>> in the module.  I would simply delete it, but I wonder if there is any
>> recommended mechanism for maintaining module versions.
>>
>> Some modules define __version__ which has a special meaning at least
>> for pydoc and possibly some third party tools.  In many cases it is
>> never updated and its format and meaning varies from module to module.
>> (For example, decimal module stores the version of the spec rather
>> than the version of the module in __version__.)
>>
>> In several instances, __version__ is set to "$Revision$" in an
>> apparent attempt to leverage VCS to keep it up to date, but this does
>> not seem to work after hg transition.  For example,
>>
>> $  ./python.exe -m pydoc pydoc
>> ..
>> VERSION
>>     $Revision$
>>
>> The other affected modules are pickle and tarfile.
>>
>> Do you have an advise on how these issues should be handled?
> MvL and I had a discussion about this at the sprint.  I am planning on writing
> an informational PEP that proposes __version__ as a standard convention.  I'd
> like to be able to do:
>
>      >>>  import foo
>      >>>  foo.__version__
>
> It won't be mandatory (thus the informational PEP), but it should be
> formalized as the preferred way to introspect a module for its version
> number.  I think there should be ways to spell this easily if the information
> is provided to packaging/distutils2 so that it can basically always be kept up
> to date without violating DRY.
>

+1

There is a minor difficulty with distutils2 which needs to be able to 
install from setup.cfg without executing code. This means it can't look 
in package.__version__ to get the version number (potentially requiring 
you to maintain __version__ both in your package and your setup.cfg).

The suggestion is that the version metadata should be created at package 
build time, defaulting to package.__version__. The rationale is that it 
is ok to execute code at build time if it removes the need for 
information duplication or for executing code at install time.

Also note that there is a proposed api for getting version info: 
pkgutil.get_version(module). Under the hood this looks for __version__ 
as one of the first places to find version info.

All the best,

Michael Foord

> -Barry
>
>
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