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From: Peter Pearson <pkpearson@nowhere.invalid>
Newsgroups: comp.lang.python
Subject: Re: Datetime timezone trouble (was: Matplotlib X-axis timezone trouble)
Date: 1 Jul 2015 19:09:03 GMT
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On Wed, 1 Jul 2015 10:55:02 -0600, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Wed, Jul 1, 2015 at 10:36 AM, Peter Pearson [wrote]:
[snip]
>> 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".
>
> Use this instead:
>
>>>> print(pacific.localize(datetime(2014, 7, 7, 12)))
> 2014-07-07 12:00:00-07:00
>
> See http://pytz.sourceforge.net/#localized-times-and-date-arithmetic

Excellent.  Thank you.

To summarize, for any similarly afflicted person who finds this thread:

 - http://pytz.sourceforge.net/#localized-times-and-date-arithmetic says:

    Unfortunately using the tzinfo argument of the standard datetime
    constructors ‘’does not work’’ with pytz for many timezones.

    It is safe for timezones without daylight saving transitions though,
    such as UTC:

 - PEP 0431 says (approximately) that datetime doesn't work as well
   as we might like with DST, but will be slow to change.

 - The "localize" function is pytz's way of working around this
   shortcoming of datetime's


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