code: def change_format(self):
      if "nyt" in self.src_file:
          ret = self.nyt10_engine()  # txt
      elif "tacred" in self.src_file:
          ret = self.tacred_engine()  # json
      else:
          raise Exception("Unsupported dataset!")
      return ret
  
imports: import json
label_desc: Use image node_id 2 for calling the format_changer obj's underlying member method code with example usage: obj.change_format() and returns: ret