code: def _get_stage_functions(cls, op: "DataFrameEwmAgg", func):
      if func == "_data_count":
          return ["_data_count"], _combine_data_count
      elif func == "mean":
          return ["cumsum", _cum_alpha_coeff_func], _combine_mean
      elif func in {"var", "std"}:
          return (
              [
                  "cumsum",
                  _cum_alpha_coeff_func,
                  "cumsum2",
                  _cum_square_alpha_coeff_func,
              ],
              _combine_var if func == "var" else _combine_std,
          )
      else:  # pragma: no cover
          raise NotImplementedError
  
imports: from collections import namedtuple
  import numpy
  import pandas
  from ....None import opcodes
  from ....serialization.serializables import BoolField, Float64Field
  from ..aggregation import BaseDataFrameExpandingAgg
label_desc: Use image node_id 6 for calling the DataFrameEwmAgg obj's underlying member method code with example usage: obj._get_stage_functions(cls, op, func) and returns: list,  _combine_data_count, list,  _combine_mean, list,  unknown