Fetch the feed if no cache exist or if cache is stale

def get(self, url, expiration):
        """
        Fetch the feed if no cache exist or if cache is stale
        """
        # Hash url to have a shorter key and add it expiration time to avoid clash for 
        # other url usage with different expiration
        cache_key = self.cache_key.format(**{
            'id': self._hash_url(url),
            'expire': str(expiration)
        })
        
        # Get feed from cache if any
        feed = cache.get(cache_key)
        # Else fetch it
        if feed is None:
            #print "No feed cache, have to fetch it"
            feed = self.fetch(url)
            cache.set(cache_key, feed, expiration)
            
        return self.parse(feed)