def _get_key(url):
    if (url not in _key_cache):
        _key_cache[url] = self.ydl.urlopen(self._prepare_url(info_dict, url)).read()
    return _key_cache[url]
def _get_key(url):
    if (url not in _key_cache):
        _key_cache[url] = self.ydl.urlopen(self._prepare_url(info_dict, url)).read()
    return _key_cache[url]