title: pip giving error ModuleNotFoundError: No module named 'enum'
body: <p>Running python 3.7.7 on Windows 7 x64.  I've just upgraded from python 2.7 and I'm trying to install the module <code>emcee</code> using <code>pip install emcee</code>.  Pip threw the error <code>ModuleNotFoundError: No module named 'enum'</code>.  I've also tried installing modules matplotlib, enum34, and numpy, but all threw the same error.  I've also tried to upgrade pip with <code>pip install --upgrade pip</code> , which again threw the same error.  I've looked into my <code>\python37\lib</code> folder, and <code>enum.py</code> is present right where it's supposed to be, but it's still not working.  </p>
  
  <p>Please help.</p>