Pass the filepath to the reload hook callbacks
I don't think you want to use autoreload for this. If two files change within half a second of each other (as is common when you do a git pull or checkout), the reload hook will only see one of them before the process restarts. I think ideally you'd use a separate PeriodicCallback to watch your js/css files and run grunt, and separately use autoreload for python files and other things that necessitate a full process restart. Or you can continue using autoreload, but recognize that it's kind of a blunt instrument and you can't tell exactly what changed.
Thanks for the feedback. I'll look into this alternative approach.