user: Question: what was the number of candidates when Leon Sacks was incumbent?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Pennsylvania 1', 'Leon Sacks', 'Democratic', 1936.0, 'Lost re-election Republican gain', 'James A. Gallagher (R) 53.5% Leon Sacks (D) 46.5%']
SQL:

assistant: SELECT COUNT("Candidates") FROM "Table" WHERE "Incumbent" = 'Leon Sacks';