code: def purge_old(self):
          '''
          Removes keys that are beyond our keep_max limit
          '''
          if self.keep_max is not None:
              keys = self.redis_conn.keys(self.get_key() + ':*')
              keys.sort(reverse=True)
              while len(keys) > self.keep_max:
                  key = keys.pop()
                  self.redis_conn.delete(keyf purge_old(self):
          '''
          Removes keys that are beyond our keep_max limit
          '''
          if self.keep_max is not None:
              keys = self.redis_conn.keys(self.get_key() + ':*')
              keys.sort(reverse=True)
              while len(keys) > self.keep_max:
                  key = keys.pop()
                  self.redis_conn.delete(key)
docs: Removes keys that are beyond our keep_max limit