code: def __next__(self):
      if self._index >= self._num_of_data:
          raise StopIteration
      _data = self._data[self._index]
      self._index += 1
      return _data
  
file_path: fastNLP/tests/helpers/datasets/normal_data.py
imports: import numpy
  import random
label_desc: Use image node_id 3 for calling the NormalSampler obj's underlying member method code with example usage: obj.__next__() and returns: _data