[Datetime-SIG] A tale of gaps, folds and leap seconds.

[Oren Tirosh]

High in the Pyrenees, on the border between Spain and France, lies the tiny
principality of Caesia. Ancient Caesian statues depict the Horae as
blindfolded and its people say that "Lady time is blind."


The prime meridian happens to pass right through Caesia, which
made Universal Time its official time. Caesia has never observed the
barbaric practice of meddling with the clock known as Daylight Savings.


When Leap Seconds were introduced, the people of Caesia devised an
ingenious plan to thwart this new abomination: they have announced that
their time zone UTC offset shall be adjusted by one second for every leap
second added to UTC.


By using the same mechanism that makes it possible for other countries to
declare an entire hour as non-existent in local time at the beginning of
Daylight Savings the people of Caesia have abolished the 61st second that
is occasionally added to the last minute of the last day of June or
December. This ensures that civilian time is still officially based on
UTC, is well-defined as a proper time zone and can even be described in the
tzfile(5) format - and yet never has a day that is not exactly 86400 SI
seconds.


Caesia had an atomic clock installed in its national labs in 1958. Their
far-sighted metrologists had already suggested then to switch its time
definition to this standard. Had they done so back in 1958, their clock
would have been numerically equivalent to TAI, before the divorce of the
second from the rotation of the Earth. However, the final ratification and
implementation of this change took a while and only came into effect in
1980. By sheer coincidence, this makes Caesia Standard Time numerically
equivalent to GPS time.


The "gaps" in conversion from Caesia Standard Time to UTC all correspond to
UTC Leap Seconds. It is well-known that gaps at one end of a timezone
conversion correspond to "folds" at the other end - a period that occurs
twice. Until recently, there was no support for folds in the datetime
library of the Python language (Caesians are avid Pythonistas). Now that
PEP495 has been implemented they are keen to check how well the datetime
library interoperates with their unusual (yet completely well-formed and
valid) time zone definition.


Can you help them?


Oren
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/datetime-sig/attachments/20161127/95bba693/attachment.html>