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Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble)

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Date Thu, 2 Jul 2015 03:08:34 +1000
Subject Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble)
From Chris Angelico <rosuav@gmail.com>
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On Thu, Jul 2, 2015 at 2:36 AM, Peter Pearson <pkpearson@nowhere.invalid> wrote:
> On Wed, 1 Jul 2015 17:15:38 +1000, Chris Angelico <rosuav@gmail.com> wrote:
>>
>> Interestingly, when I tried this (pytz version 2015.4, Python 2.7.9,
>> Debian Jessie), I saw utcoffset() showing (-1, 58020) for both. That
>> seems... odd. And I can't fault your dates - those definitely ought to
>> be easily inside and easily outside the DST boundaries. When I try
>> those dates in an unrelated time converter, they do show seven- and
>> eight- hour offsets to UTC. Maybe we're both misunderstanding the
>> meaning of utcoffset()?
>
> Here's a very simple demonstration that either something is wrong
> or I don't understand how datetime and tzinfo are supposed to work:
>
> $ python
> Python 2.7.3 (default, Mar 13 2014, 11:03:55)
>>>> from pytz import timezone
>>>> from datetime import datetime
>>>> pacific = timezone("US/Pacific")
>>>> print(datetime(2014, 7, 7, 12, tzinfo=pacific))
> 2014-07-07 12:00:00-08:00
>>>> print(datetime(2014, 1, 7, 12, tzinfo=pacific))
> 2014-01-07 12:00:00-08:00
>>>>
>
> The "-08:00" is appropriate in the second (January) case, but the
> first case is in July, and should have "-07:00".

Interesting. I poked around with the docstring for pytz.timezone and
replicated it more exactly, and this appears to work:

$ python
Python 2.7.9 (default, Mar  1 2015, 12:57:24)
[GCC 4.9.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from pytz import timezone
>>> from datetime import datetime
>>> pacific = timezone("US/Pacific")
>>> utc = timezone("UTC")
>>> print(datetime(2014, 7, 7, 12, tzinfo=utc).astimezone(pacific))
2014-07-07 05:00:00-07:00
>>> print(datetime(2014, 1, 7, 12, tzinfo=utc).astimezone(pacific))
2014-01-07 04:00:00-08:00

Clearly I do not understand what's going on here.

ChrisA

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Thread

Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-06-30 00:56 +0000
  Re: Matplotlib X-axis timezone trouble Laura Creighton <lac@openend.se> - 2015-06-30 04:03 +0200
    Re: Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-06-30 04:57 +0000
  Re: Matplotlib X-axis timezone trouble Chris Angelico <rosuav@gmail.com> - 2015-06-30 12:11 +1000
    Re: Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-06-30 04:49 +0000
      Re: Matplotlib X-axis timezone trouble Chris Angelico <rosuav@gmail.com> - 2015-06-30 17:01 +1000
        Re: Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-06-30 16:42 +0000
          Re: Matplotlib X-axis timezone trouble Chris Angelico <rosuav@gmail.com> - 2015-07-01 02:55 +1000
  Re: Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-07-01 05:50 +0000
    Re: Matplotlib X-axis timezone trouble Chris Angelico <rosuav@gmail.com> - 2015-07-01 17:15 +1000
      Datetime timezone trouble (was: Matplotlib X-axis timezone trouble) Peter Pearson <pkpearson@nowhere.invalid> - 2015-07-01 16:36 +0000
        Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble) Ian Kelly <ian.g.kelly@gmail.com> - 2015-07-01 10:55 -0600
          Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble) Peter Pearson <pkpearson@nowhere.invalid> - 2015-07-01 19:09 +0000
        Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble) Chris Angelico <rosuav@gmail.com> - 2015-07-02 03:08 +1000
  Re: Matplotlib X-axis timezone trouble Akira Li <4kir4.1i@gmail.com> - 2015-07-04 07:29 +0300
    Re: Matplotlib X-axis timezone trouble [SOLVED] Peter Pearson <pkpearson@nowhere.invalid> - 2015-07-04 17:37 +0000
  Re: Matplotlib X-axis timezone trouble Tony the Tiger <tony@tiger.invalid> - 2015-07-09 19:50 +0000
    Re: Matplotlib X-axis timezone trouble Peter Pearson <pkpearson@nowhere.invalid> - 2015-07-10 16:15 +0000

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