title: Sum list of list elements in python like sql group by
body: <p>I have a list of lists (string,integer)</p>
  
  <p>eg:</p>
  
  <pre><code>my_list=[["apple",5],["banana",6],["orange",6],["banana",9],["orange",3],["apple",111]]
  </code></pre>
  
  <p>I'd like to sum the same items and finally get this:</p>
  
  <pre><code>my2_list=[["apple",116],["banana",15],["orange",9]]
  </code></pre>