[Distutils] Specifying version information once

A. Cavallo a.cavallo at cavallinux.eu
Wed May 20 13:37:19 CEST 2009

> >
> > 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. 

No it is not that the case and I'm going to bore you probably (sorry).

The "source" dir where the module foobar is located:

$> cat ~someuser/foobar-1.0/foobar/__init__.py
__version__ = "1.0"

Assume the previous module is installed already under:

$> cat /usr/lib/python2.5/site-lib/foobar/__init__.py
__version__ = "0.9"

(please note the site-lib subidr, where all the module not belonging to the
python standard library are located).

$~someuser/foobar-1.0/> python -c 'import foobar; print foobar.__version__'
This return (or it does on my python interpreter): "1.0" not "0.9"

The case is different for the standard libraries, in fact:
$~someuser> touch os.py
$~someuser> python -c 'import os; print os.__file__'
this will return: /usr/lib/python2.5/os.py(c)

There's no need to have foobar "installed" to reflect the correct __version__.

Then we need to agree on what do we mean for install and packaging....
"python setup.py install", "python setup.py bdist_rpm/wininst" or during a 
complete deb/rpm package build?
In the latter the version the "version" is the one available in the spec/deb 
files and it cannot be reflected from the sources anyway, no matter how hard 
one try to do it.

> 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.

Finding modules can always be forced using PYTHONPATH (like in case of
foobar-1.0/src/foobar layout) or from setup.py inserting into sys.path the 
subdir: that's the easiest and in my opinion the best way to do it during 
build/install stages.


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