title: Strange Error: ZeroDivisionError: float division by zero
body: <p>I found a strange behavior and hope someone has an explanation for it.  I'm doing:</p>
  
  <pre><code>if len(list) &gt; 1 and len(list2) &gt; 1:
     total = sum(list) + sum(list2)
     result = percentage(sum(list), total)
  
  def percentage(part, whole):
      return float(part) / float(whole) *100
  </code></pre>
  
  <p>The two lists are a mix of float and int values.  I sporadically get:</p>
  
  <blockquote>
    <p>ZeroDivisionError: float division by zero</p>
  </blockquote>
  
  <p>This doesn't makes sense to me. Does anyone have an idea what's happening?</p>