code: def tensor(self, field_name, tensor_ind):
          
          if tensor_ind == self._tensor_cache_file_num[field_name]:
              return self._tensors[field_name]
          filename = self.generate_tensor_filename(field_name, tensor_ind, compressed=True)
          Tensor.load(filename, compressed=True,
                      prealloc=self._tensors[field_name])
          self._tensor_cache_file_num[field_name] = tensor_ind
          return self._tensors[field_name]
docs: Returns the tensor for a given field and tensor index.
  
          Parameters
          ----------
          field_name : str
              the name of the field to load
          tensor_index : int
              the index of the tensor
  
          Returns
          -------
          :obj:`Tensor`
              the desired tensor