    def memoize(self, obj):
        # We want hashing to be sensitive to value instead of reference.
        # For example we want ['aa', 'aa'] and ['aa', 'aaZ'[:2]]
        # to hash to the same value and that's why we disable memoization
        # for strings
        if isinstance(obj, _bytes_or_unicode):
            return
        Pickler.memoize(self, obj)