title: concurrent.futures.ProcessPoolExecutor vs multiprocessing.pool.Pool
body: <p>Please explain to me <strong>what is the difference</strong> between these two classes?</p>
  
  <ul>
  <li><a href="https://docs.python.org/3/library/concurrent.futures.html#module-concurrent.futures" rel="noreferrer">concurrent.futures.ProcessPoolExecutor</a></li>
  <li><a href="https://docs.python.org/3/library/multiprocessing.html" rel="noreferrer">multiprocessing.pool.Pool</a></li>
  </ul>
  
  <p>I noticed <code>multiprocessing</code> module existed in Python 2. But functionally?</p>