def default_from_address(self):
        """
        Cache the coinbase address so that we don't make two requests for every
        single transaction.
        """
        if self._coinbase_cache_til is not None:
            if time.time - self._coinbase_cache_til > 30:
                self._coinbase_cache_til = None
                self._coinbase_cache = None

        if self._coinbase_cache is None:
            self._coinbase_cache = self.get_coinbase()

        return self._coinbase_cache
Cache the coinbase address so that we don't make two requests for every
        single transaction.