code: def nwcsaf_old_geo_ct_filehandler(nwcsaf_old_geo_ct_filename):
      """Create a CT filehandler."""
      return NcNWCSAF(nwcsaf_old_geo_ct_filename, {}, {})
  
imports: import h5netcdf
  import numpy
  import pytest
  import xarray
  from satpy.readers.nwcsaf_nc import NcNWCSAF, read_nwcsaf_time
label_desc: Use image node_id 18 for calling a global function with example usage: nwcsaf_old_geo_ct_filehandler(nwcsaf_old_geo_ct_filename) and returns: NcNWCSAF