def _write_local_data_files(self, cursor):
        """
        Takes a cursor, and writes results to a local file.

        :return: A dictionary where keys are filenames to be used as object
            names in GCS, and values are file handles to local files that
            contain the data for the GCS objects.
        """
        schema = list(map(lambda schema_tuple: schema_tuple[0].replace(' ', '_'), cursor.description))
        file_no = 0
        tmp_file_handle = NamedTemporaryFile(delete=True)
        tmp_file_handles = {self.filename.format(file_no): tmp_file_handle}

        for row in cursor:
            # Convert if needed
            row = map(self.convert_types, row)
            row_dict = dict(zip(schema, row))

            s = json.dumps(row_dict, sort_keys=True)
            s = s.encode('utf-8')
            tmp_file_handle.write(s)

            # Append newline to make dumps BQ compatible
            tmp_file_handle.write(b'\n')

            # Stop if the file exceeds the file size limit
            if tmp_file_handle.tell() >= self.approx_max_file_size_bytes:
                file_no += 1
                tmp_file_handle = NamedTemporaryFile(delete=True)
                tmp_file_handles[self.filename.format(file_no)] = tmp_file_handle

        return tmp_file_handles
Takes a cursor, and writes results to a local file.

        :return: A dictionary where keys are filenames to be used as object
            names in GCS, and values are file handles to local files that
            contain the data for the GCS objects.