Prepares the module for processing a data batch by pulling row_sparse
        parameters from kvstore to all devices based on rowids.

        Parameters
        ----------
        param_rowids : dict of str to NDArray of list of NDArrays

def prepare_sparse_params(self, param_rowids):
        '''Prepares the module for processing a data batch by pulling row_sparse
        parameters from kvstore to all devices based on rowids.

        Parameters
        ----------
        param_rowids : dict of str to NDArray of list of NDArrays
        '''
        if not self._kvstore:
            return
        assert(isinstance(param_rowids, dict))
        for param_name, rowids in param_rowids.items():
            if isinstance(rowids, (tuple, list)):
                rowids_1d = []
                for r in rowids:
                    rowids_1d.append(r.reshape((-1,)).astype(np.int64))
                rowid = mx.nd.concat(*rowids_1d, dim=0)
            else:
                rowid = rowids
            param_idx = self._exec_group.param_names.index(param_name)
            param_val = self._exec_group.param_arrays[param_idx]
            self._kvstore.row_sparse_pull(param_name, param_val, row_ids=rowid,
                                          priority=-param_idx)