code: def __init__(self, num_of_data=100):
      self.data = list(range(num_of_data))
  
file_path: fastNLP/tests/core/samplers/test_unrepeated_sampler.py
imports: from itertools import chain
  import pytest
  from fastNLP.core.samplers import UnrepeatedRandomSampler, UnrepeatedSortedSampler, UnrepeatedSequentialSampler
label_desc: Use image node_id 1 to create a new DatasetWithVaryLength object  with example: obj = DatasetWithVaryLength(num_of_data)