user: Question: How many candidates ran against Barratt O'Hara?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Illinois 2', "Barratt O'Hara", 'Democratic', 1948.0, 'Lost re-election Republican gain', "Richard B. Vail (R) 53.6% Barratt O'Hara (D) 46.4%"]
SQL:

assistant: SELECT COUNT("Candidates") FROM "Table" WHERE "Incumbent" = 'Barratt O''Hara';