Description
Although python's datetime objects support microsecond resolution, and Time objects support sub-nanosecond resolution, conversion and arithmetic between the two can be off by tens of microseconds. (By design datetime objects do not support leap seconds, so UTC cannot be expected to work. The problems described here are for non-UTC timescales like TAI.)
Expected behavior
Computing the difference between two datetime objects then converting to a TimeDelta should give the same result as converting the datetime objects to Time objects and subtracting, to within a couple of microseconds.
Actual behavior
In fact PR #9532 demonstrates several examples where the difference exceeds 20 microseconds.
Steps to Reproduce
def test_datetime_difference_agrees_with_timedelta_no_hypothesis():
scale = "tai"
dt1 = datetime(1235, 1, 1, 0, 0)
dt2 = datetime(9950, 1, 1, 0, 0, 0, 890773)
t1 = Time(dt1, scale=scale)
t2 = Time(dt2, scale=scale)
assert(abs((t2-t1) - TimeDelta(dt2-dt1, scale=scale)) < 25*u.us)System Details
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import platform; print(platform.platform())
Linux-5.0.0-32-generic-x86_64-with-Ubuntu-19.04-disco
>>> import sys; print("Python", sys.version)
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.3.0]
>>> import numpy; print("Numpy", numpy.__version__)
Numpy 1.17.1
>>> import scipy; print("Scipy", scipy.__version__)
Scipy 1.3.1
>>> import astropy; print("astropy", astropy.__version__)
astropy 4.0.dev26780
Description
Although python's datetime objects support microsecond resolution, and Time objects support sub-nanosecond resolution, conversion and arithmetic between the two can be off by tens of microseconds. (By design datetime objects do not support leap seconds, so UTC cannot be expected to work. The problems described here are for non-UTC timescales like TAI.)
Expected behavior
Computing the difference between two datetime objects then converting to a TimeDelta should give the same result as converting the datetime objects to Time objects and subtracting, to within a couple of microseconds.
Actual behavior
In fact PR #9532 demonstrates several examples where the difference exceeds 20 microseconds.
Steps to Reproduce
System Details