Python函数返回True或1作为None,同时正确返回False和0

Question

我有一个程序进行简单的回文检查,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,我将str [0]与str [-1]进行比较,执行str [1,-1]并重复比较.我在逐步执行代码时发现的是,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'返回语句,但是当我要求它返回1时它总是返回None.但是,它正确地返回0.返回True/False时会出现相同的行为.这是我的代码.我究竟做错了什么？？

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

Answer 1

你忘了返回递归的结果.

    if first_word(s) == last_word(s) :
        return check_palin(middle(s))