issue_comments: 1287864880

The reason for this behavior is that the netcdf4 python package automatically determines the type of the attribute (NC_CHAR or NC_STRING) by attempting the conversion to ASCII: https://github.com/Unidata/netcdf4-python/issues/529 However, if the value is a byte string, no conversion is done. So, the easiest solution would be to manually encode as utf-8 and then passing the byte string to netcdf4. Unfortunately, xarray doesn't support byte strings as attribute values even though this is a valid data type for the netcdf4 engine: https://github.com/pydata/xarray/blob/6cb97f645475bddf2f3b1e1a5f24f0f9de690683/xarray/backends/api.py#L175 In the long term, I would suggest to add bytes as a supported type in that list above on xarray's side.

A quick workaround for you might be to encode the string as utf-8 and convert to a numpy array, since xarray accepts numpy arrays as data type and netcdf4 automatically extracts the data if the array contains only a single item: python ds["x"].attrs["third_str"] = np.array("hää".encode("utf-8"))