[Distutils] Specifying version information once

[Jeff Rush]

A. Cavallo wrote:
>> No, I would say “too much” here is importing a module not guaranteed to
>> be installed, for creating something as simple as a version. I'd prefer
>> the above to be::
>>
>>   $ cat _version.py
>>   # This is an auto-generated file. Use magicbean to update.
>>   version = "0.9.33"
>>   $
> 
> Or my preferred way:
>  $cat foobar/__init__.py
> __version__ = "0.9.33"
> 
> and import foobar should not trigger code execution anyway IMHO so
> $ python -c 'import foobar; print foobar.__version__'
> 0.9.33

That doesn't work in all cases.  Your example is of an external query of the
version of an installed module.  You also need to query the version -before-
it is installed (during the packaging phase) on sys.path, and also from
-within- the foobar module itself.  Your code does not handle those cases.  An
attempt to 'import foobar; print foobar.__version__' from a setup.py inside
foobar won't find foobar.

-Jeff