def METHOD_NAME(self, context=None):
    op = self.get_argument(context, index=0)
    if op is not None:
        if isinstance(op, elementpath.TypedElement):
            op = op.elem
        # This function may be invoked when the xmlschema library parses the data check schemas, in which case `op` will
        # be an object of class Xsd11Element. Only attempt to calculate the needed CLOS IDs when a real acrn-config node
        # is given.
        if hasattr(op, "xpath"):
            return len(rdt.get_policy_list(op))
    return 0