title: how to connect between tow combo boxes
body: <p>I have a dict like this:</p>
  
  <pre><code>data_dict = {'2' : [1,1], '3':[1,2], 4:[2,2], 5:[2,3]}
  </code></pre>
  
  <p>and I have 2 combo boxes, the first one has the <code>data_dict.keys()</code> and the second one has a text build from each key's list, for example <code>'1+1'</code>. now I want to connect between the combo boxes so if I choose <code>4</code> in the first combo box, the second one changes to <code>'2+2'</code>, and if I choose <code>'1+1'</code> in the second combo box, the first one changes to <code>2</code>. is there any way to do this ?</p>