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).
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)
"""
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