':type s: str
:type t: str
:rtype: bool'

def isIsomorphic(self, s, t):

    if (len(s) != len(t)):
        return False
    (s2t, t2s) = ({}, {})
    for (p, w) in izip(s, t):
        if ((w not in s2t) and (p not in t2s)):
            s2t[w] = p
            t2s[p] = w
        elif ((w not in s2t) or (s2t[w] != p)):
            return False
    return True
