Python 3.x 二项式系数-零误差除法

“主”代码用于计算每个二项系数，除非（n=k+1）。这是令人难以置信的-它说有一个零除误差，但我不明白为什么。错误发生在主功能中（d=n2/c）。知道为什么吗

def getInteger( prompt ):
    while True:
        try:
            num = int( input(prompt))
        except ValueError:
            print( "That is not an integer -- please try again")
            continue
        return num   

def factorial(f):
    f = f
    q = (f - 1)
    fac = (f * q)
    while (q) > 1:
        q -= 1
        fac = (fac * q)
    return (fac)


def main():
    n = getInteger("enter a factor:")
    k = getInteger("enter a factor:")
    while n >= k :
        n2 = factorial(n)
        k2 = factorial(k)
        a = n - k
        b = factorial(a)
        c = b * k2
        d = n2 / c
        print("n2 = {} k2 = {} a = {} b = {} c = {} d = {}" .format(n2, k2, a, b, c, d)  )
        return
    else:
        print("n must be larger than k")

if __name__ == '__main__':
    main()    

main()

---

请注意，我需要自己实现计算，因此无法使用库。

您的阶乘函数对于输入0,1不正确。这两个函数都返回0，而这两个函数都应返回1