so the basic idea is to use hython to open a scene, process it, and get some info back(in my case,“renders”). so how to get data back from subprocess.call or are there other ways to do so?
You can look into using POpen instead [stackoverflow.com]. This way you get a handle and can create a polling loop to review response from the spawned process. However, the app that you launch has to have been written to provide such feedback. Some apps, such as render engines, have a parameter you supply on launch that will trigger progress feedback information as the process runs.