[Python-Dev] Status on PEP-431 Timezones

[Alexander Belopolsky]

On Thu, Apr 9, 2015 at 11:59 AM, Isaac Schwabacher <ischwabacher at wisc.edu>
wrote:

> > Storing isdst in the datetime object would allow utcoffset(dt) to
> distinguish between 1:30AM before clock change and 1:30AM after. Where do
> you propose to store the offset?
>
> I propose to add an offset field to datetime.datetime. It should be set
> precisely when the tz field is set, and it should contain either a
> timedelta or an integer number of (possibly fractional) seconds, depending
> on what color the bikeshed gets painted. This is, IIUC, precisely where
> Lennart is proposing to store the is_dst flag.


Can you describe a situation where having isdst flag is not sufficient?

Note that in many applications you want to find the appropriate offset
knowing only local time and location, so requiring users to supply the
offset defeats the purpose of the time zone database.  In many
applications, the isdst flag can be hidden from the user.  For example, a
scheduling application can pretend that a repeated hour does not exist and
always assume that 01:30 AM is the first 01:30 AM.  (In many business
applications, it is a good idea anyways.)  Alternatively, a user attempting
to schedule an event at an ambiguous time can be presented with a warning
and a request to pick one of two possible times.  This would be a much
friendlier interface than the one always requiring the use to specify the
UTC offset.
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