def cache_rate(self, currency, date, rate):
        """
        Cache a rate for future use
        """
        if not self.is_supported(defaults.INTERNAL_CURRENCY):
            logger.info('Tried to cache unsupported currency "{}". Ignoring.'.format(currency))
        else:
            cache.set(_cache_key(currency, date), str(rate), _cache_timeout(date))
Cache a rate for future use