Palindrome Test

def isPalindrome(s):
    for i in range(len(s)//2):
        if s[i] != s[-i-1]: return False
    return True

def onlyLetters(s):
    b=s.translate(str.maketrans(dict.fromkeys(' .,?!"', None))).lower()
    return b

def isPalindromePlus(s):
    return isPalindrome(onlyLetters(s))

def isPalindromeEx(s):
    b=s.translate(str.maketrans(dict.fromkeys(' .,-?!":;', None))).lower()
    #makes table that maps punctuation to nothing, replace table in string
    #(cont'd) remove all spaces, make all letters lowercase
    return True if len(b)== 0 else True if len(b) == 1 \
    else False if b[0]!=b[-1] else isPalindromeEx(b[1:-1])