title: Datetime from year and week number
body: <p>I have a year and a week number which I want to convert into a <code>datetime.datetiem</code> object. My (naive?) reading of the documentation hinted that <code>strptime('2016 00', '%Y %W')</code> should do just that. However:</p>
  
  <pre><code>In [2]: from datetime import datetime
  
  In [3]: datetime.strptime('2016 00', '%Y %W')
  Out[3]: datetime(2016, 1, 1, 0, 0)
  
  In [4]: datetime.strptime('2016 52', '%Y %W')
  Out[4]: datetime(2016, 1, 1, 0, 0)
  </code></pre>
  
  <p>What am I doing wrong?</p>