Change of behaviour due to latest cftime

[duncanwp]

It seems that the latest version of cftime always returns cftime objects, which means that the cf-units documentation is no longer correct and the default behaviour has changed.

Specifically, the only_use_cftime_datetimes option in cftime.num2date defaults to True. I would argue that the cf-units call to this function should set this to be False for the meantime to maintain the current documented expectation that it should return python datetimes where possible. In a future major release it would be better to allow this option (and the accompanying only_use_python_datetimes option) to be passed down the call stack.

[trexfeathers]

Hi @duncanwp, I've requested some time within my team (which includes several cf-units contributors) to take a look at this. But it's difficult to tell when this will happen, so feel free to put up a PR if you have the time 🙂

[duncanwp]

Hi @trexfeathers thanks for picking this up! As fas as I can tell this will affect all calls to cftime.num2date. For example:

>>> print(type(cf_units.num2date(100, 'seconds since 1900-01-01', 'gregorian')))
<class 'cftime._cftime.real_datetime'>

Whereas this should be a datetime.datetime.