title: Python: Strange behavior of datetime.astimezone with respect to US/Pacific and America/Los_Angeles time zones?
body: <p>Please, observe:</p>
  
  <pre><code>C:\dev\poc\SDR&gt;python
  Python 2.7.1 (r271:86832, Nov 27 2010, 17:19:03) [MSC v.1500 64 bit (AMD64)] on win32
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; from pytz import timezone
  &gt;&gt;&gt; from datetime import datetime
  &gt;&gt;&gt; tz1=timezone('America/Los_Angeles')
  &gt;&gt;&gt; tz2=timezone('US/Pacific')
  &gt;&gt;&gt; ts1=datetime(2011,8,1,tzinfo=tz1)
  &gt;&gt;&gt; ts2=datetime(2011,8,1,tzinfo=tz2)
  &gt;&gt;&gt; ts1
  datetime.datetime(2011, 8, 1, 0, 0, tzinfo=&lt;DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD&gt;)
  &gt;&gt;&gt; ts2
  datetime.datetime(2011, 8, 1, 0, 0, tzinfo=&lt;DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD&gt;)
  &gt;&gt;&gt; ts1.astimezone(tz1)
  datetime.datetime(2011, 8, 1, 0, 0, tzinfo=&lt;DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD&gt;)
  &gt;&gt;&gt; ts2.astimezone(tz2)
  datetime.datetime(2011, 8, 1, 0, 0, tzinfo=&lt;DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD&gt;)
  &gt;&gt;&gt; ts1.astimezone(tz2)
  datetime.datetime(2011, 8, 1, 1, 0, tzinfo=&lt;DstTzInfo 'US/Pacific' PDT-1 day, 17:00:00 DST&gt;)
  &gt;&gt;&gt; ts2.astimezone(tz1)
  datetime.datetime(2011, 8, 1, 1, 0, tzinfo=&lt;DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST&gt;)
  &gt;&gt;&gt;
  </code></pre>
  
  <p>Here is what I do not understand. US/Pacific (<code>tz1</code>) and America/Los_Angeles (<code>tz2</code>) are supposed to denote the same time zone, aren't they? Then how come that <code>datetime.astimezone</code> called to move from one zone to another changes the hour?</p>
  
  <p>Thanks.</p>