title: sqlalchemy: dividing timedelta column by float giving strange results
body: <p>I'm trying to perform some manipulation on a column inside the query. I want to divide a timedelta column by 60. Unfortunately it is giving strange results.</p>
  
  <p>In my query I return two datetimes, the timedelta between these two datetimes, and the timedelta between these two datetimes divided by 2. An example of the output:</p>
  
  <pre><code>(datetime.datetime(2013, 1, 1, 0, 0, 8), 
  datetime.datetime(2013, 1, 1, 0, 7, 32), 
  datetime.timedelta(0, 444), 
  Decimal('362.0000'))
  </code></pre>
  
  <p>However, the timedelta 444 divided by 2 does not equal 362.0000. But this is what sqlalchemy is giving me. Is there anyway to get the correct result?</p>
  
  <p>Its important to do this manipulation in the query because I am also trying to use the above as a subquery and average over the results but I'm getting strange averages back as well.</p>
  
  <p>Here is my query:</p>
  
  <pre><code>    sub = session.query( 
                          merge.c.time_received,
                          merge.c.time_sent,
                          func.timediff(
                              merge.c.time_sent,
                              merge.c.time_received
                          ),
                          func.timediff(
                              merge.c.time_sent,
                              merge.c.time_received
                          ) / 2.0
                      ). \
                      filter(
                          merge.c.time_received != None,
                          merge.c.time_sent != None,
                      ). \
                      limit(1)
  </code></pre>