In the event that contracts are made, as provided by this act, to extend over a period longer than one year and which are to be met from current receipts of the city, it shall be lawful for the council to make an appropriation only sufficient to answer the requirements of such contract for one year, and the contract shall be legal and binding upon the city notwithstanding no appropriation has been made for the ensuing years over which the contract is to be operative. But it shall be the duty of the council to make subsequent appropriations from year to year as required for the purposes of such contracts. The obligation of the city under such contracts shall not be considered to be a part of the indebtedness of the city.
53 P.S. § 12557