Pendulum – Python datetimes made easy

Re:Pendulum – Python datetimes made easy by calpaterson on Thursday August 18, 2016 @10:14AM (#12312598)

datetime.timedelta internally uses a triple of (days,seconds,microseconds) to represent it's data and exposes that to users of the class.

That a timedelta can be represented in multiple ways is alone quite surprising but some of the representations that happen can be very confusing. I think the example I gave which represents "-1 day and a few microseconds" as "-2 days + 86399 milliseconds + 999969 microseconds" is very surprising and it commonly happens in practice.

For comparison, here's what postgres does:

    postgres=> select now() - (now() + '12 milliseconds'::interval + '1 day'::interval);
           ?column?        
    -----------------------
     -1 days -00:00:00.012
    (1 row)

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Re:Pendulum – Python datetimes made easy by sdispater on Thursday August 18, 2016 @11:08AM (#12313046)

That's a problem Pendulum is trying to solve

    d1 = datetime(2012, 1, 1, 1, 2, 3, tzinfo=pytz.UTC)
    d2 = datetime(2011, 12, 31, 22, 2, 3, tzinfo=pytz.UTC)
    delta = d2 - d1
    delta.days
    -1
    delta.seconds
    75600
    
    d1 = Pendulum(2012, 1, 1, 1, 2, 3)
    d2 = Pendulum(2011, 12, 31, 22, 2, 3)
    delta = d2 - d1
    delta.days
    0
    delta.hours
    -3

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