On Mon, Dec 12, 2011 at 4:14 PM, Lie Ryan <lie.1...@gmail.com> wrote:
> On 12/13/2011 06:46 AM, rail shafigulin wrote: > >> i found something interesting during the timedate difference calculation >> >> import datetime >> import time >> >> def main(): >> mydatetime = datetime.datetime.now() >> time.sleep(1) >> mydatetime2 = datetime.datetime.now() >> diff = mydatetime - mydatetime2 >> >> print(diff) >> >> if __name__ == '__main__': >> main() >> >> if you run this code the result you get will be >> -1 day, 23:59:59 >> >> at least that is what i'm getting. >> >> i was expecting to get -1 second. diff object is of type timedelta. this >> kind of objects represent duration, at least that is what i understood >> from the documentation >> (http://docs.python.org/**release/3.1.3/library/** >> datetime.html#timedelta-**objects<http://docs.python.org/release/3.1.3/library/datetime.html#timedelta-objects> >> ). >> so, is this a bug in the timedelta implementation or is it me not >> understanding documentation properly? >> > > It's due to timedelta normalization; in timedelta object only the day part > is ever negative, you never had negative hour, minute, or second. The `-1 > day, 23:59:59` means to subtract 1 day, then add 23:59:59; therefore giving > us -1 second. > > It is documented behavior, although perhaps hinted too subtly, from the > docs: > > """ > Note that normalization of negative values may be surprising at first. For > example, > > >>> from datetime import timedelta > >>> d = timedelta(microseconds=-1) > >>> (d.days, d.seconds, d.microseconds) > (-1, 86399, 999999) > """ > > ______________________________**_________________ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/**mailman/listinfo/tutor<http://mail.python.org/mailman/listinfo/tutor> > Thanks. You are right about the "subtle" documentation.
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