title: datetime with pytz timezone. Different offset depending on how tzinfo is set
body: <p>I ran across an interesting situation today. Can anyone explain why the offsets for ts1 and ts2 are different? ts1 is a datetime object that is timezone-aware right off the bat. ts2 is a datetime object that starts off timezone-naive and has its tzinfo replaced. However, they end up with different offsets.</p>
  
  <pre><code>&gt;&gt;&gt; from pytz import timezone
  &gt;&gt;&gt; EST = timezone('America/New_York')
  &gt;&gt;&gt; ts1 = datetime.datetime.now(tz=EST)
  &gt;&gt;&gt; ts2 = datetime.datetime.now()
  &gt;&gt;&gt; ts2 = ts2.replace(tzinfo=EST)
  &gt;&gt;&gt; print ts1
  2014-05-16 11:25:16.749748-04:00
  &gt;&gt;&gt; print ts2
  2014-05-16 11:25:19.581710-05:00
  </code></pre>