code: def tostype(self, stype):
          
          # pylint: disable= no-member, protected-access
          if stype == 'csr':
              raise ValueError("cast_storage from row_sparse to csr is not supported")
          return op.cast_storage(self, stype=stype)
docs: Return a copy of the array with chosen storage type.
  
          Returns
          -------
          NDArray or RowSparseNDArray
              A copy of the array with the chosen storage stype