[Python-Dev] PEP: New timestamp formats (original) (raw)

Victor Stinner victor.stinner at haypocalc.com
Sat Feb 4 02:38:36 CET 2012

Keep in mind timedelta has a microsecond resolution. The use cases meant for the PEP imply nanosecond resolution (POSIX' clockgettime(), for example).

datetime.datetime and datetime.timedelta can be patched to support nanosecond.

A plain number of seconds is superficially simpler, but it forces more complexity onto the user, who has to track what that number represents. If all you are doing is comparing timestamps (which I guess is most of what people do with e.g. stmtime), a number is fine. If you want the current time and date in a high-level form, you can already use datetime.now() or datetime.utcnow() (which "only" has microsecond resolution as well :-)). We don't need another way to spell it.

datetime.datetime is interesting with os.stat() if you want to display the creation, modification or last access timestamp to the user. With datetime.datime, you don't have to read the documentation to get the reference date (Epoch for os.stat(), 1970.1.1) or the timezone (UTC for os.stat()?). So datetime.datime contains two more information (start date and timezone) than int, float or Decimal cannot store.

Supporting datetime.datetime just for os.start(), whereas time.clock(), time.wallclock(), time.clock_gettime() and time.clock_getres() fail for this format, is maybe a bad idea. There is an exception: time.clock_gettime(time.CLOCK_REALTIME, timestamp=datetime.datetime) would be accept and you can get a timestamp with a nanosecond resolution... But datetime.datetime doesn't support nanosecond currently :-)

The best reason to reject datetime.datetime is that it would only "work" with some functions, whereas it would fail (with a ValueError) in most cases.

Victor

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