How to use the jsonargparse.ActionJsonnet.split_ext_vars function in jsonargparse

def _load_cfg(self, cfg_str:str, cfg_path:str='', ext_vars:dict=None, base=None) -> Dict[str, Any]:
        """Loads a configuration string (yaml or jsonnet) into a namespace checking all values against the parser.

        Args:
            cfg_str (str): The configuration content.
            cfg_path (str): Optional path to original config path, just for error printing.
            ext_vars (dict): Optional external variables used for parsing jsonnet.
            base (str or None): Base key to prepend.

        Raises:
            TypeError: If there is an invalid value according to the parser.
        """
        if self.parser_mode == 'jsonnet':
            ext_vars, ext_codes = ActionJsonnet.split_ext_vars(ext_vars)
            cfg_str = _jsonnet.evaluate_snippet(cfg_path, cfg_str, ext_vars=ext_vars, ext_codes=ext_codes)  # type: ignore
        try:
            cfg = yaml.safe_load(cfg_str)
        except Exception as ex:
            raise type(ex)('Problems parsing config :: '+str(ex))
        cfg = namespace_to_dict(_dict_to_flat_namespace(cfg))
        if base is not None:
            cfg = {base+'.'+k: v for k, v in cfg.items()}
        for action in self._actions:
            if action.dest in cfg:
                value = self._check_value_key(action, cfg[action.dest], action.dest, cfg)
                if isinstance(action, ActionParser):
                    value = namespace_to_dict(_dict_to_flat_namespace(namespace_to_dict(value)))
                    if '__path__' in value:
                        value[action.dest+'.__path__'] = value.pop('__path__')
                    del cfg[action.dest]