Question

使用Spyder Python 3.6这段代码不执行，说ispal方法没有定义。然而，当我运行它并首先输入一个整数（比如我的字符串输入= 0）时，它将运行并识别该方法。看起来我必须首先通过除了调用方法之外的分支。感谢批评。

s = input('enter a string: ')
s1 = s
s1 = s1.lower()
s1 = s1.replace(',', '')
s1 = s1.replace(' ', '')

if s1.isalpha():
    if ispal(s1) == True:
        print(s,' is a palindrome')
    else:
        print(s,' is not a palindrome')
else:
    print('you entered illegal chars')


def ispal(s1):
    if len(s1) <= 1:
        return True
    else:
        #if the first and last char are the same
        #and if all 
       return s1[0] == s1[-1] and ispal(s1[1:])

Answer 1

首先，正如TGKL指出的那样，您在定义之前调用ispal。所以在调用之前定义它，即：

def ispal(s1):
    if len(s1) <= 1:
        return True
    else:
        #if the first and last char are the same
        #and if all 
       return s1[0] == s1[-1] and ispal(s1[1:])

if s1.isalpha():
    if ispal(s1) == True:
        print(s,' is a palindrome')
    else:
        print(s,' is not a palindrome')
else:
    print('you entered illegal chars')

第二个你的回文递归函数是正确的，除非你在里面调用ispal。您应该执行ispal(s1[1:])，而不是ispal(s1[1:-1])，这将删除刚刚测试过的第一个和最后一个字符。

Answer 2

您必须首先定义您的方法，然后调用它：

s = raw_input('enter a string: ') #use raw_input so the text it takes will give to you directly a string without ""
s1 = s
s1 = s1.lower()
s1 = s1.replace(',', '')
s1 = s1.replace(' ', '')

def ispal(s1):
    if len(s1) <= 1:
        return True
    else:
        #if the first and last char are the same
        #and if all 
       return s1[0] == s1[-1] and ispal(s1[2:]) # here you put ispal(s1[1:]) it doesn't work properly :/

if s1.isalpha():
    if ispal(s1) == True:
        print(s,' is a palindrome')
    else:
        print(s,' is not a palindrome')
else:
    print('you entered illegal chars')

Python代码在首次运行时不会执行

2 个答案: