如何在密钥在REDIS中过期时获得回调

I'm developing application using Bottle. In my registration form, I'm confirming email by mail with a unique key. I'm storing this key in REDIS with expiry of 4 days. If user does not confirm email within 4 days, key gets expired. for this, I want to permanently delete the user entry from my database(mongoDB).I'm developing application using Bottle. In my