def get(self, key):
        """Get the answer associated with I{key}.  Returns None if
        no answer is cached for the key.
        @param key: the key
        @type key: (dns.name.Name, int, int) tuple whose values are the
        query name, rdtype, and rdclass.
        @rtype: dns.resolver.Answer object or None
        """

        self.maybe_clean()
        v = self.data.get(key)
        if v is None or v.expiration <= time.time():
            return None
        return v