title: Cannot import modules in Python venv
body: <p>I'm running python3 in a virtual environment, but when I try to import newly install packages, I get a <code>ImportError: No module named ...</code> error message, despite seeing that package when I run <code>!env/bin/pip3 list</code>. </p>
  
  <p>When I type <code>sys.path</code> I don't see any paths to my virtualenv:</p>
  
  <pre><code>['',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python35.zip',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/plat-darwin',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/lib-dynload',
  '/Users/zurfarosa/Library/Python/3.5/lib/python/site-packages',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages',
  '/Library/Frameworks/Python.framework/Versions/3.5/lib/python3.5/site-packages/IPython/extensions',
  '/Users/zurfarosa/.ipython',
  '/Users/zurfarosa']
  </code></pre>
  
  <p>How do I add my virtual env to my PYTHONPATH?</p>