title: attribute 'tzinfo' of 'datetime.datetime' objects is not writable
body: <p>How do I set the timezone of a datetime instance that just came out of the datastore?</p>
  
  <p>When it first comes out it is in UTC.  I want to change it to EST.</p>
  
  <p>I'm trying, for example:</p>
  
  <pre><code>class Book( db.Model ):
      creationTime = db.DateTimeProperty()
  </code></pre>
  
  <p>When a Book is retrieved, I want to set its tzinfo immediately:</p>
  
  <pre><code>book.creationTime.tzinfo = EST
  </code></pre>
  
  <p>Where <a href="http://www.python.org/doc/2.5.2/lib/datetime-tzinfo.html" rel="noreferrer">I use this example</a> for my EST object</p>
  
  <p>However I get:</p>
  
  <pre>
  attribute 'tzinfo' of 'datetime.datetime' objects is not writable
  </pre>
  
  <p>I've seen a number of answers that recommend pytz and python-dateutil, but I really want an answer to this question.</p>