[Datetime-SIG] pytz vs. PEP 495 Was: PEP-431/495

Ethan Furman ethan at stoneleaf.us
Mon Aug 24 23:35:07 CEST 2015


On 08/24/2015 02:28 PM, ISAAC J SCHWABACHER wrote:
> [ijs]
>>>> I *really* hope the answer to this one is, "don't do that".
>
> [Alexander Belopolsky]
>>> That's not an option because people already *do* [1] that and they won't stop.
>>> Neither they will stop using datetime.combine() [2] or datetime.replace() [3]
>>> or tolerate if those methods start raising exceptions.
>
> [Ethan Furman]
>> If the default is True (or False), then this won't be a problem.  It will only
>>  be None when explicitly asked for.
>>
>> `time` can just store the flag, and when it is combined with a date the flag
>>  should be checked and if None and the resulting datetime doesn't exist or is
>>  ambiguous an exception can be raised.
>
> A time with a non-constant-offset tzinfo is always ambiguous, and can have an
>  arbitrary number of possible offsets. There are several time zones with at least
>  three possible offsets for a given time in the last 10 years. How on earth do
>  you define the meaning of a time with a non-constant tzinfo attached? Or does it
>  only mean something when it's recombined with a date?

I hope the only way I would use a plain time is for today (whichever day 'today' happens to be), in which case having a tzinfo is still helpful for knowing what time it is somewhere else.  Which is 
still a buggy proposition on days involving time switches.

--
~Ethan~


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