title: python turtle event listener global variable isn't working
body: <p>I have a project, and I want the global variable <code>size</code> to change whenever you press the up arrow. This is part of my code:</p>
  
  <pre><code>size = 10
  
  def increase():
      global size
      size += 1
      print("hi")
  
  screen.onkeypress(increase, "Up")
  </code></pre>
  
  <p>but when I run the program and press the up arrow, then check <code>size</code>, it is still 10. </p>
  
  <p>Any idea why?</p>
  
  <p>Any help is appreciated. =D</p>