title: Python: how to find duplicates and sum their values?
body: <pre><code>[('Visa', 980.5), ('Rogers', 61.5), ('Visa', 215.0)]
  </code></pre>
  
  <p>for example, I have the list of tuples above, how can i find the duplicates(i.e 'Visa') and sum their values (i.e 980.5+215.0)? The output should be:</p>
  
  <pre><code>[('Visa', 1195.5), ('Rogers', 61.5)]
  </code></pre>