code: def _fetch_dataframe_step(self, step):
      return FetchDataframeStepCall(self.sql_query).call(step)
  
file_path: mindsdb/mindsdb/api/executor/sql_query/steps/map_reduce_step.py
imports: import copy
  from mindsdb_sql.parser.ast import BinaryOperation, UnaryOperation, Constant
  from mindsdb_sql.planner.steps import MapReduceStep, FetchDataframeStep, MultipleSteps
  from mindsdb.api.executor.sql_query.result_set import ResultSet
  from mindsdb.api.executor.exceptions import LogicError
  from .base import BaseStepCall
  from .fetch_dataframe import FetchDataframeStepCall
label_desc: Use image node_id 4 for calling the MapReduceStepCall obj's underlying member method code with example usage: obj._fetch_dataframe_step(step) and returns: FetchDataframeStepCall