I've just checked in experimental support for lazy, non-empty namespace packages. And what is that?, you might well ask.
Well, it seems that livinglogic.de distributes certain Python packages using a distutils kludge that allows a kind of crude namespace package to exist, without using pkg_resources. Specifically, their 'll-core' project distributes the 'll' package, and various other projects such as 'll-color' distribute modules for the 'll' package, but *without including an __init__.py*. This allows the distutils to install the modules without overwriting or duplicating the single __init__.py file.
This is an interesting approach to addressing namespace packages in a pre-setuptools world, but until now it hasn't been really usable with setuptools, for several reasons:
* pkg_resources only loaded one __init__ file for a given package
* pkg_resources couldn't import modules from a zipfile or directory with no __init__.py
* pkg_resources automatically imports registered namespace packages as soon as they're discovered, which is not a big deal for empty namespace packages, but could easily become quite problematic for ones like 'll' that contain actual code.
So, here's the solution:
* pkg_resources now loads all __init__.py's from all the distributions that provide contents for the module.
* the bdist_egg command automatically generates a dummy __init__.py for packages that don't have them. The __init__.py file contains the single line:
This ensures that the other package contents are importable, and that as soon as an import of the package occurs, it gets registered as a namespace package.
* projects that use this approach to namespace packaging must *NOT* pass a 'namespace_packages' argument to setup(), because that would cause the package to be imported even when it isn't necessary. They must also put a 'declare_namespace()' call in all of their __init__.py's, to ensure that the package will become a namespace no matter what the order of distributions on sys.path is.
Because of the complexity of this approach, I do not recommend it for new projects. Namespace packages should not have code in any of their __init__.py files, as it eliminates all of these headaches. So, this is an experimental feature intended to facilitate backward compatibility only. Don't expect it to show up in the documentation any time soon!
Anyway, I was able to get this to work for ll-core and ll-color, as long as I added a 'declare_namespace()' call like the one shown above to ll-core's __init__.py, and made them both use setuptools. I would appreciate any feedback that folks have on this.
By the way, because SourceForge CVS updating is slow, it may be a few hours before you can check out the version of setuptools that supports this. Make sure you have pkg_resources.py revision 1.69 or higher, and setuptools/command/bdist_egg.py revision 1.28 or higher, if you want to experiment. Thanks.