class_docstr: Dataset with elements chosen by a sampler
code: def __mx_handle__(self):
      if self.handle is None:
          from ._internal import MXDataset, IndexedDataset
  
          if hasattr(self._dataset, "__mx_handle__"):
              dataset = self._dataset.__mx_handle__()
          elif isinstance(self._dataset, MXDataset):
              dataset = self._dataset
          else:
              raise NotImplementedError(
                  "{} not supported.".format(self._dataset)
              )
          self.handle = IndexedDataset(
              base=dataset, indices=self._indices
          )
      return self.handle
  
imports: import os
  from ...None import recordio, ndarray
  from ...util import default_array
label_desc: Use image node_id 4 for calling the _SampledDataset obj's underlying member method code with example usage: obj.__mx_handle__() and returns: self