There shall be two Auditors of Public Accounts, who, being sworn, shall each hold office for four years and until his successor has qualified. One of said auditors shall be appointed by the General Assembly at each regular session. Said auditors shall not be of the same political party. Any vacancy occurring in the office of auditor when the General Assembly is not in session shall be filled, until the sixth Wednesday after the convening of the next session of the General Assembly, by appointment, by those members of the Joint Committee on Legislative Management who are of the same political party as that of the auditor whose office has become vacant.