How to trigger an event in web application backend?

I'm designing a Python Flask application, and want to have a program that run on the background. When something happen (such as expire of time of an object while the object itself is generated by web application), an event is triggered and change the database.

After searching i find Celery might do that, but i'm not sure. If it is the right direction, please tell me how to do that briefly. Thank you.