python 连接 appfog 的 redis 总是不成功

按照 https://docs.appfog.com/services/redis#redis-vcap 配置的

代码这样写：
os_r=os.getenv("VCAP_SERVICES")
r=redis.Redis(host=os_r['redis-2.2'][0]['credentials']['hostname'], port=os_r['redis-2.2'][0]['credentials']['port'], password=os_r['redis-2.2'][0]['credentials']['password'])

提示错误：
string indices must be integers, not str

port是 int 其他都是 str 没有问题啊