I'm not sure where the issue is, but when I specify a namespace_package in the setup.py file, I can indeed have multiple packages with the same base (foo.bar, foo.blah, etc...). The files all install in to the same directory. It drops the foo/__init__.py that would be doing the extend_path, and instead adds a ".pth" file that is a bit over my head. The problem is that it does not seem to traverse the entire sys.path to find multiple foo packages. If I do not specify namespace_packages and instead just use the pkgutil.extend_path, then this seems to allow the packages to be in multiple places in the sys.path. Is there something additional for the namespace_package that i need to specify in order for all of the sys.path to be checked? I'm using 18.5 setuptools....but I am not sure if this somehow ties in to wheel/pip, since I'm using that for the actual install.