All officers, elective and appointive, shall make oath, before some one authorized to administer oaths, that they will support the constitution of this state, and will faithfully and impartially discharge the duties of their respective offices, to the best of their skill and judgment; that they will not administer their respective offices with the aim to benefit any political party; and, in the case of councilmen, they shall add in their oath that they will not during their term of office become pecuniarily interested, directly or indirectly, in any contract with the city, or the purchase of any supplies therefor. When the officer shall have made such oath in writing and filed the same with the City Clerk, and shall have given the bond required of and accepted from him, he shall be considered as having qualified for the office to which he was elected or appointed; provided, that if any person elected to the office of mayor or councilman shall not qualify for said office as herein prescribed within ten days after he shall have been officially declared elected thereto, said office shall ipso facto become vacant, and said vacancy shall be filled in the manner provided for in this act.