While循环内的递归函数（Python）

Question

所以我正在学习 Python 中的递归，并且我有一些代码可以找到用户输入的数字的阶乘。

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

num = int(input("Enter a non-negative integer: "))
if num >= 1:
    print("The factorial of", num, "is", recursion(num))

此代码运行良好。也就是说，它将询问指定的问题，允许用户输入，并找到数字的阶乘。所以我想要做的是把递归函数放在 While 循环中，这样在程序打印提交的数字的阶乘后，它会询问用户是否想输入另一个数字。

loop = 1
while loop == 1:

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

num = int(input("Enter a non-negative integer: "))
if num >= 1:
    print("The factorial of", num, "is", recursion(num))
    print()
    answer = input(print("Would you like to find the factorial of another non-negative integer? Y/N: "))
    if answer == "Y":
        loop = 1
    else:
        loop = 0

我在使用此代码时遇到的问题是，它会询问用户输入数字、查找阶乘并提出问题“您想查找另一个非负整数的阶乘吗？Y/N :" 但是当我在 IDLE 中运行时，上述问题后面的行显示“无”。

Python 3.5.0 (v3.5.0:374f501f4567, Sep 13 2015, 02:27:37) 
[MSC v.1900 64 bit (AMD64)] on win32
Type "copyright", "credits" or "license()" for more information.
Enter a non-negative integer: 6
The factorial of 6 is 720
Would you like to find the factorial of another non-negative integer? Y/N: 
NoneY
Enter a non-negative integer: 4
The factorial of 4 is 24
Would you like to find the factorial of another non-negative integer? Y/N: 
NoneN
>>> 

我查看了Python documentation (section 4.6)，它提到解释器通常会抑制“无”。

1. 为什么当我在 IDLE 中运行它时，它会在循环控制问题之后显示“None”？
2. 有没有办法省略“None”并仍然使用 print()？

Answer 1

您之所以看到None，是因为您的input 中有一个print：

input(print("Would you like to find the factorial of another non-negative integer? Y/N: "))

删除print

input("Would you like to find the factorial of another non-negative integer? Y/N: ")

Answer 2

这一行：

answer = input(print("Would you like to find the factorial of another non-negative integer? Y/N: "))

print 返回None，因此您将None 输入到阶乘函数中，然后将None 作为答案。

应该是：

answer = input("Would you like to find the factorial of another non-negative integer? Y/N: ")