4层嵌套的Json，如何扁平化？

def flatten_json(json_data, parent_key='', sep='.'):
    flattened_data = {}
    for key, value in json_data.items():
        new_key = parent_key + sep + key if parent_key else key
        if isinstance(value, dict):
            flattened_data.update(flatten_json(value, new_key, sep=sep))
        else:
            flattened_data[new_key] = value
    return flattened_data

{
  "a": {
    "b": {
      "c": {
        "d": "value"
      }
    }
  }
}

{
  "a.b.c.d": "value"
}