The new NON_NANOSECOND_WARNING is not very nice to end users

[hmaarrfk]

What is your issue?

The new nanosecond warning doesn't really point anybody to where they should change their code.

Nor does it really tell them how to fix it.

import xarray as xr
import numpy as np
xr.DataArray(np.zeros(1, dtype='datetime64[us]'))

yields

xarray/core/variable.py:194: UserWarning: Converting non-nanosecond precision datetime values to nanosecond precision. This behavior can eventually be relaxed in xarray, as it is an artifact from pandas which is now beginning to support non-nanosecond precision values.

xarray/xarray/core/variable.py

Line 194 in f32d354

warnings.warn(NON_NANOSECOND_WARNING.format(case="datetime"))

I think at the very least, the stacklevel should be specified when calling the warn function.

It isn't really pretty, but I've been passing a parameter when I expect to pass up a warning to the end user:
eg. vispy/vispy#2405

However, others have not liked that approach.

[djhoese]

Sorry for dragging this issue up again, but even with the new warning message I still have some questions. Do I have to switch to nanosecond precision times or will xarray/pandas/numpy just figure it out when I combine/compare times with different precisions?

[spencerkclark]

For the time being xarray should behave as it always has, converting any non-nanosecond precision times to nanosecond-precision before being used internally.

[djhoese]

And with new pandas (which I understand as being the thing/library that is changing) and new xarray, what will happen? What happens between nano and non-nano times?

[spencerkclark]

Xarray will convert any non-nanosecond precision times to nanosecond precision (or an error will be raised if this is not possible).

[spencerkclark]

For a little more discussion of this issue see #7493. As the example at the top of the issue notes, there is at least one place where non-nanosecond times can slip in (this is not intentional), but for most code pathways xarray should currently convert things automatically.