title: find and update a value of a dictionary in list of dictionaries
body: <p>How can I find the <code>dictionary</code> with value <code>user7</code> then update it's <code>match_sum</code> eg add 3 to the existing 4.</p>
  
  <pre><code>l = [{'user': 'user6', 'match_sum': 8}, 
          {'user': 'user7', 'match_sum': 4}, 
          {'user': 'user9', 'match_sum': 7}, 
          {'user': 'user8', 'match_sum': 2}
         ]
  </code></pre>
  
  <p>I have this, and am not sure if its the best practice to do it.</p>
  
  <pre><code>&gt;&gt;&gt; for x in l:
  ...     if x['user']=='user7':
  ...         x['match_sum'] +=3
  </code></pre>