[Python-Dev] datetime nanosecond support

[Christian Heimes]

Am 25.07.2012 03:46, schrieb Guido van Rossum:
> First you will have to show how you'd have to code this *without*
> nanosecond precision in datetime and how tedious that is. (I expect
> that representing the timestamp as a long integer expressing a posix
> timestamp times a billion would be very reasonable.)

I'd vote for two separate numbers, the first similar to JDN (Julian Day
Number [1]), the second for nanoseconds per day. 3600 * 1000000 fit
nicely into an unsigned 32bit int. This approach has the neat benefit
that we'd get rid of the timestamp_t limitations and year 2038 bug at
once. IIRC datetime used to break for dates before 1970 on some system
because timestamp_t was unsigned. Python could finally support dates BC!

JDN is widely used by astronomers and historians to supports a wide
range of years as well as convert between calendar systems. Its day 0 is
January 1, 4713 BC in proleptic Julian calendar. The conversion between
Julian and Gregorian calendar makes JDN hard to use. Rata Die (Januar 1,
1 AD at midnight in proleptic Gregorian calender) sounds like a good idea.

People in need for a high precision timer should also consinder TAI [2]
instead of UTC as TAI doesn't have leap seconds. DJB's daemontools
specifies a tai64n log format [3] that is similar to your idea.

Christian

[1] http://en.wikipedia.org/wiki/Julian_Day_Number
[2] http://en.wikipedia.org/wiki/International_Atomic_Time
[3] http://cr.yp.to/daemontools/tai64n.html