ceiling_key(d, 1)
ceiling_key(d, 2)
ceiling_key(d, 4)
ceiling_key(d, 3)
ceiling_key(d, 2)
ceiling_key(d, 1)
ceiling_key(d, 0)
ceiling_key(d, 6)
floor_key(d, 6)
floor_key(d, 7)
floor_key(d, 101)
floor_key(d, 100)
python: retrieving ceiling key and floor key in a dictionary or a set