递归数求和程序返回“无”作为Python中的总和

Question

我正在努力学习递归，并编写了这段代码来返回从一个到所选数字的所有数字的总和。 当我运行程序时，无论我最初输入什么数字，它给我的总和总是“无”，我的意思是，我的程序中outputSum变量的值似乎是“无”。 我认为改变SUM_OF_NUMBERS的初始化值可能会改变这一点，但事实并非如此，我仍然将“无”作为输出。 任何人都可以指向我的代码中导致此错误的部分吗？

def sumOfNumbers(number):

    SUM_OF_NUMBERS = 0

    if number > 0:
        SUM_OF_NUMBERS = SUM_OF_NUMBERS + number
    else:
        return SUM_OF_NUMBERS

    number = number - 1

    sumOfNumbers(number)

def main():

    repeat = 'Y'
    outputSum = 0

    while repeat == 'Y' or repeat == 'y':    
        print("Welcome to the Sum Of Numbers program!")
        number = int(input("\nPlease enter a number to sum up: "))

        outputSum = sumOfNumbers(number)

        print("\nThe sum of all numbers from 1 to " + str(number) + \
              " is " + str(outputSum))

        repeat = input("\nWould you like to sum up another number?" \
                       '\nEnter "Y" for "YES" or "N" for "NO": ')

        if repeat == 'N' or repeat == 'n':
            print("\nThank you for using the program.")
        else:
            print("\nSorry, that was not a valid option.")
            repeat = input('Please enter "Y" for "YES" or "N" for "NO": ')

main()

Answer 1

由于在输入大于0时没有返回任何内容，因此您获得了None 。

比你拥有的要简单得多。

def sumOfNumbers(number):
    if number > 0:
        return number + sumOfNumbers(number-1)
    else:
        return 0

Answer 2

def sumOfNumbers(n):
  if n>0:
    return n+sumOfNumbers(n-1)
  else:
    return 0

i = input("Enter a number")
print "Sum of numbers:",sumOfNumbers(i)

Answer 3

或者，只需预先测试边界条件和处理（尾部）递归，

def sumOfNumbers(number):
    if number <= 0: return 0
    return number+sumOfNumbers(number-1)

Answer 4

你的逻辑是合理的。 问题是您每次都将SUM_OF_NUMBERS重置为0。 此外，它返回None，因为您忘记了最终的return语句。 要解决此问题，您可以将其作为参数传递，如：

def sumOfNumbers(number, SUM_OF_NUMBERS = 0):

    if number > 0:
        SUM_OF_NUMBERS = SUM_OF_NUMBERS + number
    else:
        return SUM_OF_NUMBERS

    number = number - 1

    return sumOfNumbers(number, SUM_OF_NUMBERS)

Answer 5

有两件小事：

1. 你的函数什么都不返回
2. 每次调用该函数时都设置SUM_OF_NUMBERS = 0。

只是为了简化这里的简短代码：

def recursive_sum(num):
  if num == 0:
    return 0
  return num + recursive_sum(num-1)