我的Python代码包含递归函数有什么问题？

Question

我正在使用递归来找到一个快乐的数字.

以下是我的Python代码:

deepth = 0
def is_happy_number(number):
    astring = str(number)
    global deepth
    digits = [int(char) for char in astring]
    sum_digit = sum([digit**2 for digit in digits])
    if sum_digit == 1:
        deepth = 0
        return True
    else:
        deepth += 1
        if deepth >800:
            return False
    return is_happy_number(sum_digit)

print '7',is_happy_number(7)
for number in range(1,11):
    print number,is_happy_number(number)

结果是:

7 True
1 True
2 False
3 False
4 False
5 False
6 False
7 False
8 False
9 False
10 True

当我单独测试7号时,它返回'True'.当我运行最后两个原始代码时,数字7返回'False'.

我不知道哪个部分是错的.

几分钟后,我在Python代码中找到了错误的部分.我补充说:

deepth = 0

后:

if deepth > 800:

随着@Will的提醒,我找到了另一个解决这个问题的方法.修改代码如下:

def is_happy_number(number, deepth=0):
    astring = str(number)
    digits = [int(char) for char in astring]
    sum_digit = sum([digit**2 for digit in digits])
    if sum_digit == 1:
        return True
    else:
    deepth += 1
    if deepth >800:
        return False
    return is_happy_number(sum_digit,deepth)

print '7',is_happy_number(7,0)
for number in range(1,10):
    if is_happy_number(number,0):
        print number,

Answer 1

您无法重置全局变量depth.处理此问题的更好方法是将深度传递给递归调用.

像这样的东西:

def is_happy_number(number, depth=0):
    # ... as before ...
    return is_happy_number(sum_digit, depth)

Answer 2

正如巴拉克马诺斯在他的回答中指出的那样,deepth变量就是罪魁祸首.在达到深度800的情况下不会重置.如果这样做,您的代码将起作用:

deepth = 0

def is_happy_number(number):
    astring = str(number)
    global deepth
    digits = [int(char) for char in astring]
    sum_digit = sum([digit**2 for digit in digits])
    if sum_digit == 1:
        deepth = 0
        return True
    else:
        deepth += 1
        if deepth >800:
            deepth = 0
            return False

    return is_happy_number(sum_digit)

print '7',is_happy_number(7)
for number in range(1,11):
    print number,is_happy_number(number)

我完全同意威尔你不应该使用全局变量.