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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 _get_pid_file_variable(self, db):
 """ Get the `pid_file` variable """

        pid_file = None
        try:
            with closing(db.cursor()) as cursor:
                cursor.execute("SHOW VARIABLES LIKE 'pid_file'")
                pid_file = cursor.fetchone()[1]
        except Exception:
            self.warning("Error while fetching pid_file variable of MySQL.")

        return pid_file