title: Spyder and Python Debug: can not set breakpoint
body: <p>I am not able to add breakpoints in my spyder IDE with Python3.6</p>
  
  <p>I have tried restarting my computer, but neither with <code>F12</code>nor by clicking on <code>Debug -&gt; Set/Clear breakpoint</code> let's me enter a breakpoint. Could anybody explain what I am doing wrong? I am sure this is a stupid error. </p>
  
  <p>I am running Spyder 3.1.2 on a Windows 10. </p>
  
  <p>Thanks.</p>