方法一：for循环

def factorialFunc(n):
    x = 1
    for i in range(1, n+1):
        x *= i
    return x

方法二：递归 5x4x3x2x1

def factorialFunc(n):
    if n == 1:
        return 1
    else:
        return n * factorialFunc(n-1)

方法三：reduce()配合lambda函数

from functools import reduce
def factorialFunc(n):
    return reduce(lambda x,y:x*y, range(1, n+1))

方法四：math.factorial()直接求

import math
print(math.factorial(5))