Installing python 3.6 namespace package in site-packages directory structure

Question

Problem:

I cannot get a source distribution namespace package to install in a 3.6.4 virtual environment in the directory structure expected (under Lib/site-packages).

Background:

I'm working with namespace packages in 2 different versions of python.

When I build the package in 2.7.14 using pkgutils style ns packaging, I can install and the directory structure is rolled out how I want it to.

When I build the package in 3.6.4, the package installs, but the directory structure is not created as expected.

Setup:

I have 2 virtual environments.

In the working one, I'm using the 2.7.14 compatible pkgutils namespace package functionality. I'm using virtualenv for this virtual environment to confirm installation, and it installs as I wish. The directory structure shows up in my venv/Lib/site-packages as expected, such that venv/Lib/site-packages/tools/sub_a exists.

In the non-working one, I'm using venv and implicit namespace packaging per PEP420

Here is my 3.6.4 package directory structure:

tools
  -sub_a
   -__init__.py
   -module.py
setup.py
README.rst

my subpackage init only has the following inside:

name = 'sub_a'

Here is my setup.py

from setuptools import setup
from codecs import open
from os import path

here = path.abspath(path.dirname(__file__))

with open(path.join(here, 'README.rst'), encoding='utf-8') as f:
    long_description = f.read()

setup(

name='tools-sub-a',
version='1.0.0',
description='A sample Python project',
long_description=long_description,
url='none',
author='myuser',
author_email='myuser@host.com',
classifiers=[
    'Development Status :: 3 - Alpha',
    'Intended Audience :: Developers',
    'Topic :: Software Development :: Build Tools',
    'License :: Only For Internal Use',
    'Programming Language :: Python :: 3.6.4'
],

keywords='none',
packages=['tools.sub_a'],
install_requires=[],
extras_require={},
package_data={},
data_files=[],
entry_points={},
project_urls={},
)

The package builds using python setup.py sdist, I transfer the tar.gz file over to the virtual environment directory root, and run

pip install --no-index --find-links=. tools-sub-a

This installs fine, however when I navigate to the virtual environment Lib/site-packages directory, the tools/sub_a directory structure is not there.

I see a tools_sub_a-1.0.0.dist-info, but none of the expected namespace package directories.