How to use the stingray.crossspectrum.Crossspectrum function in stingray

def save_to_intermediate_file(stingray_object, fname):
    """Save Stingray object to intermediate file."""
    from stingray.lightcurve import Lightcurve
    from stingray.events import EventList
    from stingray.crossspectrum import Crossspectrum
    from hendrics.io import save_lcurve, save_events, save_pds
    if isinstance(stingray_object, Lightcurve):
        save_lcurve(stingray_object, fname)
    elif isinstance(stingray_object, EventList):
        save_events(stingray_object, fname)
    # This also work for Powerspectrum and AveragedCrosspowerspectrum, clearly
    elif isinstance(stingray_object, Crossspectrum):
        save_pds(stingray_object, fname)
    else:
        logging.error("save_to_intermediate_file: Unknown object type: %s" % type(stingray_object).__name__)
        return False

    return True

# This will return an EventList, a light curve, a Powerspectrum, ...
    # depending on the contents of the file
    try:
        ftype, contents = get_file_type(fname)
    except:
        contents = _retrieve_pickle_object(fname)

    if isinstance(contents, Lightcurve):
        return DataSet.get_lightcurve_dataset_from_stingray_Lightcurve(contents)

    elif isinstance(contents, EventList):
        return DataSet.get_eventlist_dataset_from_stingray_Eventlist(contents)

    # This also work for Powerspectrum and AveragedCrosspowerspectrum, clearly
    elif isinstance(contents, Crossspectrum):
        logging.error("Unsupported intermediate file type: Crossspectrum")

    else:
        logging.error("Unsupported intermediate file type: %s" % type(stingray_object).__name__)

    return None