def delete(self, doc):
        if doc.id is None:
            raise DatabaseException('Document does not have id')
        if doc.sid is None:
            try:
                rs = self.db.docs.remove({'id': doc.id}, safe=True)
                assert rs['n'] == 1
            except Exception as e:
                raise DatabaseException(e)
            return None
        doc.data = None
        return self.update(doc)
def sls(n, d):
            gg = te.reduce_axis((0, lengths[n]))
            indices_idx = length_offsets[n] + gg
            data_idx = indices[indices_idx]
            data_val = data[data_idx, d]
            return te.sum(data_val, axis=gg)