Determines if the cache files have expired, or if it is still
        valid

def is_cache_valid(self):
        ''' Determines if the cache files have expired, or if it is still
        valid '''

        if os.path.isfile(self.cache_path_cache):
            mod_time = os.path.getmtime(self.cache_path_cache)
            current_time = time()
            if (mod_time + self.cache_max_age) > current_time:
                if os.path.isfile(self.cache_path_index):
                    return True

        return False