title: Unexpected behavior after running python setup.py install inside virtualenv
body: <p>Here's my directory structure for reference.</p>
  
  <pre><code>|- package1
  |   '- abc.py
  |- setup.py
  |- examples
  |   '- directory1
  |         '- run.py
  |- venv
  </code></pre>
  
  <p>After running <code>python setup.py install</code>, I see that a <code>package1.egg</code> file is placed successfully in <code>venv/lib/python*/site-packages</code>. When I run <code>pip list</code> the output contains the <code>package1</code> entry with the correct version as described in the <code>setup.py</code> file. </p>
  
  <p>Now, when I try to run <code>python examples/directory1/run.py</code> the first line of which is <code>import package1</code>, I get an error <code>ModuleNotFoundError: No module named 'package1'</code>. I get the same error when I launch the python interpreter and try to import <code>package1</code> too.</p>
  
  <p>What could I be doing wrong?</p>