code: def __str__(self):
      data_info = "\nContaining:\n"
      for data_key in self._data_dict.keys():
          data_info += data_key + "\n"
      return data_info
  
imports: from recbole.evaluator.register import Register
  import torch
  import copy
label_desc: Use image node_id 9 for calling the DataStruct obj's underlying member method code with example usage: obj.__str__() and returns: data_info