code: def to_json(self):
      
      new_pos = self._blob_reader.tell()
      if self._has_iterated:
        new_pos -= 1
      return {self.BLOB_KEY_PARAM: self._blob_key,
              self.INITIAL_POSITION_PARAM: new_pos,
              self.END_POSITION_PARAM: self._end_position}
docs: Returns an json-compatible input shard spec for remaining inputs.