title: How to iterate through a list and sum members together
body: <p>Using Python 3.3, I have a list as such:</p>
  
  <pre><code>&gt;&gt;&gt; ls
  [250313, 242517, 243788, 1606025, 1566365, 1573483]
  </code></pre>
  
  <p>I need a <code>for</code> loop or built-in function to iterate over this, summing three integers together at a time.</p>
  
  <p>I would like the end result to look like this:</p>
  
  <pre><code>&gt;&gt;&gt; newls 
  [736618, 4745873]
  </code></pre>
  
  <p>It seems like <code>itertools</code> or <code>sum</code> would be helpful for this, but I can't seem to figure it out yet.</p>