code: def from_json(cls, json):
      
      return cls(
          namespace_range.NamespaceRange.from_json_object(
              json[cls.NAMESPACE_RANGE_PARAM]),
          json[cls.BATCH_SIZE_PARAM])
docs: Create new DatastoreInputReader from the json, encoded by to_json.
  
      Args:
        json: json map representation of DatastoreInputReader.
  
      Returns:
        an instance of DatastoreInputReader with all data deserialized from json.