code: def samples_by_indices_nomapping(self, indices):
          
          if not self._random_access:
              raise TypeError('samples_by_indices_nomapping method not '
                              'supported as one or more of the underlying '
                              'data sources does not support random access')
          if not isinstance(indices, tuple):
              raise TypeError('indices should be a tuple, not a {}'.format(
                  type(indices)
              ))
          dataset_index, sample_indices = indices
          ds = self.datasets[dataset_index]
          return ds.samples_by_indices_nomapping(sample_indices)
docs: Gather a batch of samples by indices *without* applying any index
          mapping.
  
          Parameters
          ----------
          indices: a tuple of the form `(dataset_index, sample_indices)`
              The `dataset_index` identifies the dataset from which to draw
              samples while `sample_indices` identifies the samples to draw
              from it.
  
          Returns
          -------
          nested list of arrays
              A mini-batch