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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _save(self):
 """Save the model to a .csv file """

        # if not first time saving, copy .csv to a backup
        if os.path.isfile(self._full_filename):
            shutil.copyfile(self._full_filename, self._full_backup_filename)

        # write to csv
        with open(self._full_filename, 'w') as file:
            writer = csv.DictWriter(file, fieldnames=self._headers)
            writer.writeheader()
            for row in self._table:
                writer.writerow(row)