code: def reduction_func(request):
      """
      yields the string names of all groupby reduction functions, one at a time.
      """
      return request.param
  
file_path: pandas/pandas/tests/groupby/conftest.py
imports: import numpy
  import pytest
  from pandas import DataFrame, Index, Series, date_range
  from pandas.core.groupby.base import reduction_kernels, transformation_kernels
label_desc: Use image node_id 7 for calling a global function with example usage: reduction_func(request) and returns: request