title: sum of datetime.datetime object gave an error TypeError: unsupported operand type(s) for +: 'datetime.datetime' and 'datetime.datetime'
body: <p>I'm trying to sum a list of datetime.datetime object using :</p>
  
  <pre><code>from datetime import datetime, timedelta
  d= [datetime.datetime(2013, 5, 1, 9, 31, 24), datetime.datetime(2013, 6, 11, 17, 22, 18), datetime.datetime(2013, 4, 3, 16, 6, 59)]
  
  sum_d = sum(d, timedelta())
  </code></pre>
  
  <p>I get the error :</p>
  
  <p><code>TypeError: unsupported operand type(s) for +: 'datetime.datetime' and 'datetime.datetime'</code></p>
  
  <p>any idea what am I doing wrong or how I can sum up this list?</p>
  
  <p>I want to get the average of this list I was thinking about:</p>
  
  <pre><code> d_avg = sum(d, timedelta()) / len(d)
  </code></pre>
  
  <p>Thanks!</p>