code: def _get_stage_functions(cls, op: "DataFrameExpandingAgg", func):
      if func == "_data_count":
          return ["count"], _combine_arithmetic
      elif func in ("sum", "prod", "count"):
          return [func], _combine_arithmetic
      elif func in ("min", "max"):
          return [func], partial(_combine_minmax, fun_name=func)
      elif func == "mean":
          return ["sum", "count"], _combine_mean
      elif func in {"var", "std"}:
          return (
              ["sum", "count", "var"],
              _combine_var if func == "var" else _combine_std,
          )
      else:  # pragma: no cover
          raise NotImplementedError
  
imports: from collections import namedtuple
  from functools import partial
  import numpy
  import pandas
  from ....None import opcodes
  from ....serialization.serializables import BoolField
  from ..aggregation import BaseDataFrameExpandingAgg
label_desc: Use image node_id 3 for calling the DataFrameExpandingAgg obj's underlying member method code with example usage: obj._get_stage_functions(cls, op, func) and returns: list,  _combine_arithmetic, list,  _combine_arithmetic, list,  partial, list,  _combine_mean, list,  unknown