TypeError: Invalid value for attr 'freq’ When I save SPI-6 to nc files

[CGL5230]

Generic Issue

• xclim version:0.46.0
• Python version:3.11.0
• Operating System:Linux

Description

I got thoes error When I try to save the SPI-6. By the way, I want to calculate the SPI-6 by the command, It's correct?
pr_AWI_CM_ssp585 is a daily dataset for Cmip6 model output including the 'pr' variable.

What I Did

AWI_CM_ssp585_SPI = xclim.indicators.atmos.standardized_precipitation_index(pr='pr',freq='MS',ds=pr_AWI_CM_ssp585,window=6)
AWI_CM_ssp585_SPI.to_netcdf('/home/cgl/workdir/AWI_CM_ssp585_SPI.nc')

What I Received

TypeError: Invalid value for attr 'freq': None. For serialization to netCDF files, its value must be of one of the following types: str, Number, ndarray, number, list, tuple

[coxipi]

Hi @CGL5230,

Thanks for reporting this. I confirm this bug, some attributes have values that are problematic when saving to netcdf. In the case of freq, it should not have been None in the first place, even if netcdf accepted this, so it's good to know, it's also a bookkeeping error. In the meantime, you can just replace all problematic values with an empty string. You can add this code between your two lines:

for k in AWI_CM_ssp585_SPI.attrs.keys():
    if AWI_CM_ssp585_SPI.attrs[k] is None or AWI_CM_ssp585_SPI.attrs[k] == {}:
        AWI_CM_ssp585_SPI.attrs[k] = ""

Specifically for freq, you can add back the value you used if that's useful for you, that is what the SPI function will do when it's repaired

AWI_CM_ssp585_SPI.attrs["freq"] = "MS"

Alternatively, if you save to zarr, there is no problem like this.

And yes, you have the correct code for SPI-6!

[CGL5230]

Hi@coxipi ,
Thanks for quick reply. The solution is I save the value of the SPI-6 dataset to new variable. The suggestion you offer is great!