Fixed #20722 -- Fixed MemcachedCache backend get_many on Python 3.

        self._cache.delete(key)

    def get_many(self, keys, version=None):

        new_keys = map(lambda x: self.make_key(x, version=version), keys)

        new_keys = [self.make_key(x, version=version) for x in keys]

        ret = self._cache.get_multi(new_keys)

        if ret:

            _ = {}