List 9 python

list9.py

def checkValidlist9AB(n):
    a = n // 10
    b = n % 10
    return (a != b)


def checkValidlist9(n):
    return (n > 9 and n < 100)


def list9(n):
    if n == 9:
        print(9)
    else:
        a = n // 10
        b = n % 10
        print(n)
        return list9(abs((b * 10 + a) - n))


x = int(input("n ? "))

if checkValidlist9(x):
    if checkValid9AB(x):
        list9(x)
    else:
        print(0)
else:
    print("The number you gave is invalid")