[tz] Transitions after those included in zoneinfo binaries?

Bradley White bww at acm.org
Wed Dec 13 20:39:54 UTC 2017

On Wed, Dec 13, 2017 at 3:26 PM, Paul G <paul at ganssle.io> wrote:

> I recently noticed a discrepancy between the python-dateutil and pytz
> libraries when calculating offsets for dates after the last included
> transition in the zonefile binaries. What it boils down to is that when it
> runs out of transitions, python-dateutil selects the "standard" offset and
> pytz assumes that after the last transition the value "holds". In the
> southern hemisphere, this produces two different behaviors.
> Obviously there's no "right" answer here, since these are predictions
> about what time zones will be applied 20 years in the future (and even if
> the rules stayed the same, the "end date" is entirely artificial). Still, I
> wonder if it might be worth a bit of discussion and possibly a note in the
> Theory file? Barring a representation of the data that exposes the rules
> directly (in which case no such artificial limitation would be necessary),
> ...

Does not the "POSIX-TZ-environment-variable-style string for use in
handling instants after the last transition time stored in the file"
specify exactly what to do?

> I think either fallback is defensible.
> Best,
> Paul
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