I'm strongly with Antoine on this. If you use context manager as a decorator you should be able to reuse it - and in general both generators and context managers can be reused and so I don't understand the phrase 'moral equivalent of the implicit context manager'.

If having APIs that can be used as context managers *and* decorators is a useful thing (and usage in django, py.test and mock seems to show that it is) then this functionality should be provided.