title: Python turtle: check if a key is down
body: <p>I want to be able to detect if a key is currently down.</p>
  
  <p>I have found the <code>turtle.onkey</code> and <code>turtle.onkeypress</code> functions, however these don't work for me for two reasons:</p>
  
  <ol>
  <li>they are only triggered when the key is pressed or released. </li>
  <li>they call a function when you run them. </li>
  </ol>
  
  <p>I want a boolean that is <code>True</code> if the key is held down,  or <code>False</code> if the key is not held down.</p>