code: def calculate_keys_by_mapreduce_state(cls, mapreduce_state):
      if mapreduce_state is None:
        return []
      keys = []
      for i in range(mapreduce_state.mapreduce_spec.mapper.shard_count):
        shard_id = cls.shard_id_from_number(mapreduce_state.key().name(), i)
        keys.append(cls.get_key_by_shard_id(shard_id))
      return keys