code: def num_rows(self) -> int:
      return (
          self._builder.num_rows() if self._builder is not None else 0
      )
  
file_path: ray/python/ray/data/_internal/delegating_block_builder.py
imports: import collections
  from typing import Any, Mapping
  from ray.data._internal.arrow_block import ArrowBlockBuilder
  from ray.data._internal.block_builder import BlockBuilder
  from ray.data._internal.pandas_block import PandasBlockBuilder
  from ray.data.block import Block, BlockAccessor, DataBatch
label_desc: Use image node_id 7 for calling the DelegatingBlockBuilder obj's underlying member method code with example usage: obj.num_rows() and returns: unknown