The petition, when signed by the requisite number of registered voters, shall be filed with the city clerk. The city clerk shall attach thereto a certificate setting forth the name and address of the person or persons filing the petition in his office and the date when the petition was filed. A copy of the petition, exclusive of signatures, together with the certificate shall be entered in a record book to be kept for that purpose in the office of the city clerk. Any defect in the form of the petition or record as kept by the city clerk shall not invalidate the same.