def set(self, prefix, url, obj):
        """ Add an object into the cache """
        if not self.cache_dir:
            return

        filename = self._get_cache_file(prefix, url)

        try:
            os.makedirs(os.path.join(self.cache_dir, prefix))
        except OSError:
            pass

        with open(filename, 'wb') as file:
            pickle.dump(obj, file)
Add an object into the cache