code: def preprocess(self, data_group):
      # Toy function for base class.
  
      self.output_data = data_group.preprocessed_case
      data_group.preprocessed_case = self.output_data
  
imports: import os
  import numpy
  from deepneuro.utilities.util import add_parameter, replace_suffix, cli_sanitize, docker_print
  from deepneuro.utilities.conversion import read_image_files, save_data
label_desc: Use image node_id 6 for calling the Preprocessor obj's underlying member method code with example usage: obj.preprocess(data_group) without return types