code: def datapoint_indices_for_tensor(self, tensor_index):
          
          if tensor_index >= self._num_tensors:
              raise ValueError('Tensor index %d is greater than the number of tensors (%d)' %(tensor_index, self._num_tensors))
          return self._file_num_to_indices[tensor_index]
docs: Returns the indices for all datapoints in the given tensor.