CREATE OR REPLACE FUNCTION Add_to_stroke(my_stroke VARCHAR(50))
RETURNS VOID
AS $$
    BEGIN
        INSERT INTO stroke VALUES (my_stroke);
    END $$
LANGUAGE plpgsql
VOLATILE;

conn = psycopg2.connect("dbname=postgres user=postgres password=psswd")
cur = conn.cursor()
cur.callproc('Add_to_stroke','freestyle')

ProgrammingError: function add_to_stroke(unknown, unknown, unknown, unknown, unknown, unknown, unknown, unknown, unknown) does not exist
    LINE 1: SELECT * FROM add_to_stroke('f','r','e','e','s','t','y','l',...
                      ^
HINT:  No function matches the given name and argument types. You might need to add explicit type casts.

SELECT Add_to_stroke('Freestyle')

foo = 'Freestyle'
 cur.execute("SELECT add_to_stroke(%s)",(foo,))