Python函数返回True或1作为None,同时正确返回False和0

2024-03-29 00:10:37 发布

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我有一个程序,它做一个简单的回文检查,通过比较字符串的每一端,然后递归地执行原始字符串的子字符串。也就是说,我比较str[0]和str[-1],做str[1,-1]并重复比较。我在单步执行代码时发现,当我要求函数check_palin()返回1时,它返回None。我可以清楚地看到它“执行”return语句,但当我要求它返回1时,它总是不返回任何值。但是,它正确返回0。返回True/False也可以观察到相同的行为。这是我的密码。我做错什么了??在

def check_palin(s):
    global init
    print("Init is %d" %(init))
    if len(s) <= 1 :
        if not init :
            print("returning 1")
            return True
        else :
            print("Please supply a string of atleast 2 characters! Exiting...\n")
            print("returning 0")
            return False
    else :
        init = 0
        if first_word(s) == last_word(s) :
            check_palin(middle(s))
        else :
            print("returning 0")
            return False


def first_word(s) :
    return s[0]

def last_word(s):
    return s[-1]

def middle(s):
    return s[1:-1]

init  = 1
s = raw_input("Please enter a string")
print(check_palin(s))
if not check_palin(s) :
    print ("String %s IS NOT a palindrome!" %(s))
else :
    print ("String %s IS a palindrome!" %(s))

Output:
Please enter a stringababa
Init is 1
Init is 0
Init is 0
returning 1
None
Init is 0
Init is 0
Init is 0
returning 1
String ababa IS NOT a palindrome!

Process finished with exit code 0

Tags: 字符串falsereturnifinitisdefcheck