Python: Strange behavior of datetime.astimezone with respect to US/Pacific and America/Los_Angeles time zones?
datetime, python, timezone
Solution
Daylight Savings Time. Notice that the last two entries are listing `PDT-1`.
`astimezone` takes into account DST, but only if it actually goes through its full logic.
The first two `astimezone` calls in your example don't go through the full logic, because they short-circuit (since the timezone they're converting "to" already matches the one they're converting "from").
(You might wonder why the initial datetimes aren't using PDT already. This is because the `datetime` constructor doesn't take into account daylight savings time, even if you pass it a timezone - it just sets the timezone blindly.)
Problem
Please, observe: ``` C:\dev\poc\SDR>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. >>> from pytz import timezone >>> from datetime import datetime >>> tz1=timezone('America/Los_Angeles') >>> tz2=timezone('US/Pacific') >>> ts1=datetime(2011,8,1,tzinfo=tz1) >>> ts2=datetime(2011,8,1,tzinfo=tz2) >>> ts1 datetime.datetime(2011, 8, 1, 0, 0, tzinfo=<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>) >>> ts2 datetime.datetime(2011, 8, 1, 0, 0, tzinfo=<DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD>) >>> ts1.astimezone(tz1) datetime.datetime(2011, 8, 1, 0, 0, tzinfo=<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>) >>> ts2.astimezone(tz2) datetime.datetime(2011, 8, 1, 0, 0, tzinfo=<DstTzInfo 'US/Pacific' PST-1 day, 16:00:00 STD>) >>> ts1.astimezone(tz2) datetime.datetime(2011, 8, 1, 1, 0, tzinfo=<DstTzInfo 'US/Pacific' PDT-1 day, 17:00:00 DST>) >>> ts2.astimezone(tz1) datetime.datetime(2011, 8, 1, 1, 0, tzinfo=<DstTzInfo 'America/Los_Angeles' PDT-1 day, 17:00:00 DST>) >>> ``` Here is what I do not understand. US/Pacific (`tz1`) and America/Los_Angeles (`tz2`) are supposed to denote the same time zone, aren't they? Then how come that `datetime.astimezone` called to move from one zone to another changes the hour? Thanks.