s = [50, 62, 15, 76, 57, 97, 82, 99, 45, 23]
x = dict([(a, 'A++' if a > 75 else 'A' if a > 55 else 'F') for a in s])
print(x)
{(97): 'A++', (45): 'F', (99): 'A++', (76): 'A++', (82): 'A++', (15): 'F',
    (50): 'F', (23): 'F', (57): 'A', (62): 'A'}
Convert numbers to grades in python list