Comment 4 for bug 619294

When the builder installs the package (setup.py install --single-version-externally-managed, and more specifically, setuptools' install_lib command), __init__.py files are skipped, because they would conflict if installed by multiple packages . Instead, setuptools' install_egg_info command installs a *-nspkg.pth file that ensures that the package exists -- if an __init__.py file exists, it is used, but if not, a module is added to sys.modules, so imports work anyway. Since all zope projects use setuptools, they don't need the __init__.py files.

I can add a virtual python-zope.app to some random package, because I can't think of the most important zope.app.* library like zope.interface is. But I would like to avoid depending on python-zope.app at all, that's why I filed this bug.