Section 137. The city clerk shall not declare the result of an election for city officers or of a vote upon any question submitted to the voters until the time for filing a petition for a recount of ballots has expired, or, if such petition has been filed, until the ballots have been recounted and the returns amended, notwithstanding any special act relating to the city. After the ballots have been recounted and the records amended, the city clerk shall forthwith declare the result of the election, and shall thereupon issue certificates of their election to the persons elected. No person elected to a city office shall act in an official capacity by virtue of such election before his certificate of election has been issued.