was there a district attorney?
Yes, Richardson Dilworth
1951 Philadelphia municipal election
As in the mayor's race, the contest for district attorney pitted a Democratic reformer, Richardson Dilworth, against a representative of the Republican machine, Michael A. Foley. 
who was the mayor during the 1951 philadelphia municipal election? UNANSWERABLE
wiki:25079509
1951 Philadelphia municipal election [SEP] District Attorney
Philadelphia elects a district attorney independently of the mayor, in a system that predates the charter change. Since 1957, district attorney elections have followed mayoral and city council elections by two years, but in 1951 both offices were up for election in the same year. As in the mayor's race, the contest for district attorney pitted a Democratic reformer, Richardson Dilworth, against a representative of the Republican machine, Michael A. Foley. Dilworth, like Clark, was a former Republican who had been advocating reform for several years. He had run for mayor unsuccessfully in 1947, with Clark as his campaign manager.