For the purpose of paying the cost of sidewalk improvements in any sidewalk district, the mayor and council or board of trustees shall have the power and may, by ordinance, cause to be issued bonds of the city or village, to be called Sidewalk Bonds of District No. ...., payable in not exceeding six years from date, and to bear interest annually or semiannually, with interest coupons attached. Such bonds shall be general obligations of the city or village, with principal and interest payable from a fund made up of the special assessments collected and supplemented by transfers from the general fund to make up any deficiency in the collection of the special assessments. For the purpose of making partial payments as the work progresses, warrants bearing interest may be issued by the mayor and council, or the board of trustees, upon certificate of the engineer in charge showing the amount of the work completed and materials necessarily purchased and delivered for the orderly and proper continuance of the project, in a sum not exceeding ninety-five percent of the cost thereof, which warrants shall be redeemed and paid upon the sale of the bonds issued and sold as aforesaid. The city or village shall pay to the contractor interest, at the rate of eight percent per annum on the amounts due on partial and final payments, beginning forty-five days after the certification of the amounts due by the engineer in charge and approval by the governing body and running until the date that the warrant is tendered to the contractor.