xarray netcdf changing datatype when saving

Question

When I save an xarray dataset, it is changing the datatypes of the variables when saving (or possibly when loading back in). I am not able to produce a minimal working example, because I have no idea what's causing this change (the many others I have saved have worked fine).

My original dataset looks like:

mytest4
Out[177]:
<xarray.Dataset>
Dimensions:  (lat: 93, lon: 87, name: 31, time: 82)
Coordinates:
  * time     (time) datetime64[ns] 2019-01-01 2020-01-01 ... 2100-01-01
  * lat      (lat) float32 -10.824516 -10.788528 ... -7.532379 -7.4960403
  * lon      (lon) float32 -79.47869 -79.44204 -79.40539 ... -76.36327 -76.32662
  * name     (name) <U14 'ACCESS1-0' 'ACCESS1-3' ... 'bcc-csm1-1' 'inmcm4'
Data variables:
    pr       (name, time, lat, lon) float64 nan nan nan nan ... nan nan nan nan

I then save it using

mytest4.to_netcdf(ETCCDI_folder+'test4.nc')

Open it again

mytest5=xr.open_dataset(ETCCDI_folder+'test4.nc')

And now it looks like this:

mytest5
Out[180]:
<xarray.Dataset>
Dimensions:  (lat: 93, lon: 87, name: 31, time: 82)
Coordinates:
  * time     (time) datetime64[ns] 2019-01-01 2020-01-01 ... 2100-01-01
  * lat      (lat) float32 -10.824516 -10.788528 ... -7.532379 -7.4960403
  * lon      (lon) float32 -79.47869 -79.44204 -79.40539 ... -76.36327 -76.32662
  * name     (name) object 'ACCESS1-0' 'ACCESS1-3' ... 'bcc-csm1-1' 'inmcm4'
Data variables:
    pr       (name, time, lat, lon) timedelta64[ns] ...

where the 'name' coordinate and more importantly the 'pr' variable have changed datatype. If I use ncview to view 'test4' directly in ETCCDI_folder, it looks as I'd expect, but once loaded back into python it becomes nonsense. Can anyone help?

Answer 1

1. Review all options for xr.open_dataset() , in particular decode_times and decode_timedelta
2. If necessary, use the encoding dict option in xr.to_netcdf() -- see http://xarray.pydata.org/en/stable/generated/xarray.Dataset.to_netcdf.html
3. Is there are reason your name var is unicode and not regular strings? I don't believe NetCDF supports unicode strings as a datatype.