> FYI, mxDateTime test the C lib for leap second support; if leap > seconds are used, then it has to support these too in conversions > from and to Unix ticks. Since AFAIK POSIX doesn't admit the existence of leap seconds, how do you ask the C library for leap seconds? > > BTW, I doubt there'd be any discussion of leap seconds in the C > > std if some astronomers hadn't been early Unix users. It's never > > a net win in the end to try to make a scientist happy <0.9 wink>. Yeah, we learned that the hard way by adding complex numbers. :-) > What strange about leap seconds is that they don't fit well with > the idea of counting seconds since some fixed point in history. > They are only useful for conversions from this count to a broken > down date and time representation.... time simply doesn't > leap. > > >From a comment in mxDateTime: > /* This function checks whether the system uses the POSIX time_t rules > (which do not support leap seconds) or a time package with leap > second support enabled. Return 1 if it uses POSIX time_t values, 0 > otherwise. > > POSIX: 1986-12-31 23:59:59 UTC == 536457599 > > With leap seconds: == 536457612 > > (since there were 13 leap seconds in the years 1972-1985 according > to the tz package available from ftp://elsie.nci.nih.gov/pub/) > > */ I think an important (but so far unvoiced) requirement is that datetime objects can be stored in a database. Since the database may be read by systems that may or may not support leap seconds, we should be independent of the leap second support in the C library. As I've said before, we should ignore leap seconds. Even if we end up expressing times deltas as a number of seconds, that should be understood to be calendar seconds and not astronomical seconds. Let the astronomers deal with leap seconds themselves -- they should know how to. BTW, this means that we can't use the C calls mktime(), timegm(), localtime(), and gmtime(), or their Python wrappers in the time module! That's fine by me. --Guido van Rossum (home page: http://www.python.org/~guido/)
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