title: Why is pip editable install causing issue with subpackages?
body: <h2>The Problem</h2>
  
  <p>I'm having an issue using editable install for my package. Inside my package I have three subpackages as shown in my setup.py file. Everything works fine if I install with <code>pip install .</code>, but if I install with <code>pip install -e .</code> then I'll get the following error when attempting to run the CLI <code>relctl</code>:</p>
  
  <pre><code>Traceback (most recent call last):
    File "/Users/my_username/.virtualenvs/rawp3/bin/relctl", line 11, in &lt;module&gt;
      load_entry_point('tech-control', 'console_scripts', 'relctl')()
    File "/Users/my_username/.virtualenvs/rawp3/lib/python3.7/site-packages/pkg_resources/__init__.py", line 490, in load_entry_point
      return get_distribution(dist).load_entry_point(group, name)
    File "/Users/my_username/.virtualenvs/rawp3/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2859, in load_entry_point
      return ep.load()
    File "/Users/my_username/.virtualenvs/rawp3/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2450, in load
      return self.resolve()
    File "/Users/my_username/.virtualenvs/rawp3/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2456, in resolve
      module = __import__(self.module_name, fromlist=['__name__'], level=0)
  ModuleNotFoundError: No module named 'tech_control.cli'
  </code></pre>
  
  <p>On further inspection I find that I'm not able to import any subpackages. E.g. The following will fail:
  <code>import tech_control.boards</code>
  Fails with: <code>ModuleNotFoundError: No module named 'tech_control.boards'</code></p>
  
  <h2>My Package Directory</h2>
  
  <pre><code>tech_control/
  ├── __init__.py
  ├── boards
  │   ├── __init__.py
  │   ├── board_base.py
  │   ├── tech8ch.py
  │   └── wiring.py
  ├── cli
  │   ├── __init__.py
  │   └── cli.py
  └── setup.py
  </code></pre>
  
  <h2>Setup.py</h2>
  
  <pre class="lang-py prettyprint-override"><code>from setuptools import setup
  
  setup(
      name="tech_control",
      version="0.1.0",
      description="CLI for Tech Boards",
      packages=["tech_control", "tech_control.boards", "tech_control.cli"],
      package_dir={
          "tech_control": "",
          "tech_control.boards": "boards",
          "tech_control.cli": "cli"},
      install_requires=["pyusb"],
      entry_points={
          "console_scripts": [
              "relctl = tech_control.cli.cli:main"
          ]
      },
  )
  </code></pre>
  
  <h2>Question</h2>
  
  <p>Why is my editable install preventing me from accessing subpackages?</p>