阶乘

1、手写

def Foo(x):
    if (x==1):
        return 1
    else:
        return x*Foo(x-1)
print(Foo(4))

 2、系统库函数


　　math.factorial(4)

3、for循环

def foo(n):
    result = 1
    for i in range(1,n+1):
        if i == 1:
            result = 1
        else:
            result = i * result
    return result
foo(4)