title: Multiple choices command line argument
body: <p>How could a multiple choices argument in the command line be implemented? There would be a predefined set of options and the user can choose multiple:</p>
  
  <pre><code>python cli.py --alphabet upper,lower,digits,symbols
  </code></pre>
  
  <p>or</p>
  
  <pre><code>python cli.py --alphabet upper lower digits symbols
  </code></pre>