class_docstr: Base class for MNIST, cifar10, etc.
code: def _get_data(self):
      raise NotImplementedError
  
imports: import os
  from ...None import recordio, ndarray
  from ...util import default_array
label_desc: Use image node_id 4 for calling the _DownloadedDataset obj's underlying member method code with example usage: obj._get_data() without return types