title: In Jupyter, how to avoid extra command lines at bottom of notebook?
body: <p>Symptom looks like this:
  <a href="https://i.stack.imgur.com/BJiTo.png" rel="nofollow noreferrer">View of what the extra lines look like</a></p>
  
  <p>After iterating on a single line while developing, clicking 'Alt-Enter' to execute, the console accumulates these extra lines.
  Is there a way to avoid this?</p>