最长回文子串

def longestPalindrome(str):
    s=list(str)
    maxlen=0
    pos=0
    for i in range(len(s)):
        low=i-1
        high=i+1
        while low>=0 and high<len(s):
            if s[low]==s[high]:
                low-=1
                high+=1
            else:
                break
        if i-low-1>maxlen:
            maxlen=i-low-1
            pos=i
    return(pos,maxlen)