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 _prepare_streams(self) -> None:
        if self._write_stream is not None:
            return
        if self.filename:
            filepath = os.path.join(self.dirpath, self._prepare_filename())
            fs = get_filesystem(filepath)
            file = fs.open(filepath, "a")
            self._output_file = file
            self._write_stream = file.write
        else:
            self._write_stream = self._rank_zero_info