code: def _get_reducer_operand(subtask_chunk_graph):
      return next(
          c.op
          for c in subtask_chunk_graph
          if isinstance(c.op, MapReduceOperand)
          and c.op.stage == OperandStage.reduce
      )
  
file_path: mars/mars/services/task/execution/ray/shuffle.py
imports: import numpy
  from typing import List, Iterable
  from .....core.operand import MapReduceOperand, OperandStage
  from .....utils import lazy_import
  from ....subtask import Subtask, SubtaskGraph
label_desc: Use image node_id 1 for calling a global function with example usage: _get_reducer_operand(subtask_chunk_graph) and returns: next