# -*- coding: utf-8 -*-

from functools import reduce

x = str(input("请输入四位数或者三位数的数字： "))
times = 1
while True:

    max_math = sorted(x,reverse=True)
    min_math = sorted(x)
    max_math_switch_str = int(reduce(lambda x,y:x+y,max_math))
    min_math_switch_str = int(reduce(lambda x,y:x+y,min_math))

    s = max_math_switch_str-min_math_switch_str
    print("now",times,max_math_switch_str,"-",min_math_switch_str,"=",s)

    if s == 6174:
        break
    if s == 495:
        break

    x = str(s)
    times += 1

• 注：6174是黑洞数（亦称为卡布列克常数，任何非四位相同数字，只要将数字重新排列，组合成最大的值和最小的数再加以相减，重复以上步骤，七次以内就会出现6174。例如：8045，8540-0458=8082，8820-0288=8532，8532-2358=6174。还有一个数字是495）