code: def __init__(self, data_len=1000):
      super(MyDataset, self).__init__()
      self.data = [jittor.ones((3, 4)) for _ in range(data_len)]
      self.set_attrs(total_len=data_len)
      self.dataset_len = data_len
  
file_path: fastNLP/tests/core/dataloaders/jittor_dataloader/test_fdl.py
imports: import pytest
  import numpy
  from fastNLP.envs import _module_available
  from fastNLP.core.dataloaders.jittor_dataloader import JittorDataLoader, prepare_jittor_dataloader
  from fastNLP.core.dataset import DataSet
  from fastNLP.core.collators import Collator
  from fastNLP.io.data_bundle import DataBundle
  from fastNLP.envs.imports import _NEED_IMPORT_JITTOR
label_desc: Use image node_id 1 to create a new MyDataset object from inherited base classes: Dataset with example: obj = MyDataset(data_len)