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Hello,

I'm having similar issues. However, I'm creating a dataset from a dict (data are packed in Matlab file).

The dataset is ds_ivt and I have tried: python ds_ivt.time.encode['units'] = 'days since 1900-01-01' and

python ds_ivt.to_netcdf('ds_ivt.nc',encoding={'time':{'units':'days since 1900-01-01'}}) The .info() method retrieves:

bash ds_ivt.info() xarray.Dataset { dimensions: lat = 161 ; lon = 291 ; time = 1460 ; variables: float32 lat(lat) ; lat:units = degrees ; float32 lon(lon) ; lon:units = degrees ; datetime64[ns] time(time) ; time:units = days since 1900-01-01 ; float32 iqu(time, lat, lon) ; iqu:units = kg m-1 s-1 ; float32 iqv(time, lat, lon) ; iqv:units = kg m-1 s-1 ; // global attributes: }

Thanks - It turns out the workaround is to open the file with decoding_times = False

Is this a bug, or a feature?

In the notebook, those variables called time and time2 are not datetime objects (I demonstrate that). In fact, there are no datetime objects in the Notebook's scope, unless you count the CF time variable that is part of the open Dataset. And yet, time and time2 seem to be treated as such when the dataset is written to a file. Or, is it that the CF time in the Dataset is getting re-encoded somehow in spite of encoding=None? Why would that fail? Would you explain what is going on here?

I have updated my gist with the .info() information here:
https://gist.github.com/anonymous/ff055f732029585605b965f282685d73

@mmartini-usgs The here comes up because your time variables have dtype datetime64. There are two ways to handle this: - If you don't want xarray to convert from datetime64 to numbers when saving the netCDF file, you need to convert the data yourself to a float or integer array. - If you do want to make use of xarray's automated conversion, you need to specify units in encoding instead of attrs.

If something else seems to be going on, please share the result of calling .info() on your dataset.

I think I have a similar problem.

I have a netCDF file with CF time. I'm trying to add two variables with a different kind of time (EPIC time, time2). These variables should not be datetime. They should be ordinary numbers.

Even when I don't include any units, it chokes on "units". Even with encoding = None ValueError: Failed hard to prevent overwriting key 'units' The gist is here: https://gist.github.com/anonymous/4614dfb55778cd0d51427daf6503cd8c

It's a time specific thing, because if I do the same operation with a different variable in the same file (read a variable, do something with it, then save it) it works fine. One clue is that it still carries the attributes (generally desired behavior) to the new file. But my EPIC time and time2 above, if they NOT datetime and have NO attributes... should work the same way.

This could be my misunderstanding of xarray and time operations, I'm a python newbie, if so I would appreciate someone setting me straight. It's preventing me from using xarray.

Thanks!

Yes, you can control this by setting encoding, e.g., time.encoding['units'] = 'days since '1900-01-01' http://xarray.pydata.org/en/stable/io.html#time-units

It looks like this error message is not very helpful currently -- a PR to improve it would be appreciated!