title: pipenv not working after Mac OS Catalina update err: 'original_python' referenced before assignment
body: <p>I am trying to use pipenv as follows</p>
  <pre><code>pipenv install dash==1.17.0
  </code></pre>
  <p>and getting  a selection of errors including</p>
  <pre><code>Creating virtual environment...Using base prefix '/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.8'
  
  UnboundLocalError: local variable 'original_python' referenced before assignment
  
  Failed to create virtual environment.
  </code></pre>