Pendulum – Python datetimes made easy

Post by calpaterson » Thu, Aug 18, 2016, 2:14 PM UTC

jbg_ wrote: post #60

calpaterson wrote: post #37

Earlier quoted context omitted.

>>> from datetime import datetime, timedelta >>> datetime.now() - (datetime.now() + timedelta(days=1)) datetime.timedelta(-2, 86399, 999969)

I’m not entirely sure what you were trying to demonstrate, but clearly the result of datetime.now() changes between the two invocations (it has microsecond precision). Try: >>> from datetime import datetime, timedelta >>> now = datetime.now() >>> now - (now + timedelta(days=1)) datetime.timedelta(-1)

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

Post by sdispater » Thu, Aug 18, 2016, 3:08 PM UTC

calpaterson wrote: post #71

jbg_ wrote: post #60

Earlier quoted context omitted.

I’m not entirely sure what you were trying to demonstrate, but clearly the result of datetime.now() changes between the two invocations (it has microsecond precision). Try: >>> from datetime import datetime, timedelta >>> now = datetime.now() >>> now - (now + timedelta(days=1)) datetime.timedelta(-1)

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 v…

    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

Post by ak217 » Sun, Aug 21, 2016, 10:04 PM UTC

dvl wrote: post #59

ak217 wrote: post #10

Earlier quoted context omitted.

So far I haven't seen either of these libraries do substantially better than datetime+dateutil+pytz at anything they claim to be good at.

I'm happy to not have to import 3 libraries anymore (2 that aren't part of standard library) to see if one date is greater than another or to add few days to a date.