The problem -
You don't have to write your own decorator for this as
user_passes_test is already included in Django.
And there's a snippet (
group_required_decorator) that extends this decorator and which should be pretty appropriate for your use case.
If you really want to write your own decorator then there's a lot of good documentation on the net.
And well, to (re-) use the decorator just put your decorator in a module on your path and you can import it from any other module.