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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_db_versions(self, conn):
 """ Get all the versions stored in the database as a set. :param conn: a DB API 2 connection """

        curs = conn.cursor()
        query = 'select version from {}'.format(self.version_table)
        try:
            curs.execute(query)
            return set(version for version, in curs.fetchall())
        except:
            raise VersioningNotInstalled('Run oq engine --upgrade-db')