Python 3.7.4 (default, Aug 13 2019, 15:17:50)
[Clang 4.0.1 (tags/RELEASE_401/final)] :: Anaconda, Inc. on darwin
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>>> import cftime
>>> dt = cftime.datetime(2020, 1, 1, calendar="julian")
>>> from datetime import timedelta
>>> dt += timedelta(hours=1)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +=: 'cftime._cftime.datetime' and 'datetime.timedelta'
>>> cftime.__version__
'1.2.1'
cftime.datetimereturns an object of typecftime._cftime.datetime, which cannot be added to or subtracted from using atimedelta. Based on itscalendarkeyword argument, I would expect it to return a subclass such asDatetimeJulianwhich has arithmetic defined.