125. Valid Palindrome(判断忽略标点的字符串是否回文，加个正则，与上一题解法一样)

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

 class Solution:
     def isPalindrome(self, s):
         """
         :type s: str
         :rtype: bool
         """
         if s=='':
             return True
         import re
         x = re.sub('\W','',s).lower()
         if x=='':
             return True
         if(len(x)%2!=0):#数
             for i in range(int(len(x)/2)+1):
                 if(x[i]!=x[len(x)-i-1]):
                     return False
         else:
             for i in range(int(len(x)/2)+1):
                 if(x[i]!=x[len(x)-i-1]):
                     return False
         return True