递归

def count_down(i):
    print(i)
    if i <=0:
        return "倒计时到此结束"
    else:
        count_down(i-1)

print(count_down(10))

def fact(x):
    if x==1:
        return 1
    else:
        return x * fact(x-1)

print(fact(6))

def test_depth(x):
    x +=1
    print("第%d次运行"%x)
    test_depth(x)

fact(0)