Remember to set the 'grid' where needed

Use case: I want to download some daily ERA5 data from 'reanalysis-era5-complete'.

If you do not set 'grid' in your script, then you will get the default reduced Gaussian grid GRIB file.

If you want to download data in NetCDF, then make sure you have both 'format' and 'grid' set. If you don't set 'grid', you will not get what you want.

#!/usr/bin/env python
import cdsapi
 
c = cdsapi.Client()
c.retrieve('reanalysis-era5-complete', { 
    #......
    'grid'    : '1.0/1.0', # Latitude/longitude grid in degrees: east-west (longitude) and north-south resolution (latitude). Default: reduced Gaussian grid
    'format'  : 'netcdf', # Default: grib
}, 'xxx.nc')

Full examples are available from How to download ERA5.

For ERA5 data hosted on the CDS, you are recommended to apply the same principle although the data was pre-interpolated to a lat-lon grid.