Disallow standard calendar np.datetime64 encoding prior to reform
#10352
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@spencerkclark +1 to have the user decide. |
kmuehlbauer
approved these changes
May 26, 2025
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Sounds good—thanks @kmuehlbauer—I'll merge this in so we can move forward with #8324. |
spencerkclark
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In #9618 we allowed encoding
np.datetime64values prior to 1582-10-15 using a"standard"or"gregorian"calendar through cftime. While technically possible, this implicitly introduces a calendar change, and means the values can no longer be round tripped asnp.datetime64—xarray will choosecftime.DatetimeGregorianinstances when decoding instead. I am not sure how often this will come up and the behavior may not be the user's intent.This PR switches to raising a
ValueErrorin this circumstance, and recommends encoding with a"proleptic_gregorian"calendar instead (the calendar that xarray automatically chooses fornp.datetime64values if provided no user input).cc: @kmuehlbauer (this is one possible way to address the issue in #8324)
whats-new.rst