title: How to sum the unique keys in dictionary?
body: <p>I have a bunch of key values in a list:</p>
  
  <pre><code>all = [('a' : '87'), ('b': '72'), ('a' : '39'), ('b' : '84')]
  </code></pre>
  
  <p>How can I quickly sum up all of the values that have the same keys?</p>
  
  <p>Output:</p>
  
  <pre class="lang-none prettyprint-override"><code>a = 126
  b = 156
  </code></pre>