[Python-ideas] Happy leap second

Guido van Rossum guido at python.org
Sat Jun 30 20:04:51 CEST 2012

There's no reason why you need to use date time objects for such extreme
use cases.

--Guido van Rossum (sent from Android phone)
On Jun 30, 2012 10:17 AM, "Alexander Belopolsky" <
alexander.belopolsky at gmail.com> wrote:

> On Sat, Jun 30, 2012 at 12:29 PM, Guido van Rossum <guido at python.org>
> wrote:
> ..
> > The roundtrip requirement is telling though -- they have no way to
> > actually represent a leap second in the underlying clock (which is a
> > POSIX timestamp).
> This correct: POSIX gettimeofday() cannot produce accurate UTC time
> during the leap second, but this does not mean that a python program
> should not be able to keep UTC time as accurately as the underlying
> hardware allows.  Systems synchronized with official time using NTP,
> get notifications about leap seconds up to a day in advance and can
> prepare for a second during which NTP time stops.  (As far as I
> understand, few systems actually stop their clocks or roll them back
> on a leap seconds - most slow the clocks down in various incompatible
> ways.)  For example, during the leap second a software clock can use
> clock_gettime() (or Python's new time.monotonic()) function to get
> actual time.
> For better worse, legal time throughout the world is based on UTC and
> once every couple of years there is a second that has to be
> communicated as hh:mm:60.  Today we are fortunate that it is inserted
> during the time when most of the world markets are closed, but next
> time we may see a lot of lawsuits between traders arguing over whose
> orders should have been filled first.  While few systems report
> accurate UTC time during a leap second, there is no technological
> limitation that would prevent most systems from implementing it.  One
> can even implement such UTC clock in python, but valid times produced
> by such clock cannot be stored in datetime objects.
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