code: def from_json(cls, json):
      
      key_range_iter_cls = _KEY_RANGE_ITERATORS[json["key_range_iter_cls"]]
      obj = cls(key_ranges.KeyRangesFactory.from_json(json["key_ranges"]),
                model.QuerySpec.from_json(json["query_spec"]),
                key_range_iter_cls)
  
      current_iter = None
      if json["current_iter"]:
        current_iter = key_range_iter_cls.from_json(json["current_iter"])
      # pylint: disable=protected-access
      obj._current_iter = current_iter
      return obj
docs: Inherit doc.