user: Question: How many different partners played in the finale in 1973?
Columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Partner', 'Opponents in the final', 'Score in the final']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 1971.0, 'US Open', 'Grass', 'Bob Maud', 'Billie Jean King Owen Davidson', '6–3, 7–5']
SQL:

assistant: SELECT COUNT("Partner") FROM "Table" WHERE "Year" = 1973.0;