python3 两层dict字典转置

dictss = {
        10: {3: 1,  4: 2,  5:  3, 6: 4,  7: 5,  8: 6,   9: 7,   10: 8,  11: 9,  12: 10, 13: 11, 14: 12, 15: 13, 16: 14, 17: 15, },
        20: {3: 16, 4: 17, 5: 18, 6: 19, 7: 20, 8: 21,     9: 22,     10: 23, 11: 24,    12: 25,    13: 26, 14: 27,    15: 28, },
}

rev_dictss = {}
for (k, v) in dictss.items():
    # print(dict(v))
    for vk, vv in v.items():
        # print(vv, vk)
        rev_dictss[vv] = k

print(rev_dictss)