The only real necessary restriction on the @ operator is that its argument be callable and take a single argument. Many expressions could return a callable object. Why not let them? Is it really worth having a special case just to SyntaxError expressions that sometimes won't result in an appropriate callable?
Things someone might want to do, ordered roughly from most reasonable to least reasonable ;) @foo().bar() @foo or bar @mydecorators['foo'] @lambda f: foo(f) or bar(f)
Why disallow these forms? It seems quite difficult, especially, to explain why the first one does not, or should not, work.
I have a gut feeling about this one. I'm not sure where it comes from, but I have it. It may be that I want the compiler to be able to recognize certain decorators.
So while it would be quite easy to change the syntax to @test in the future, I'd like to stick with the more restricted form unless a real use case is presented where allowing @test would increase readability. (@foo().bar() doesn't count because I don't expect you'll ever need that).
--Guido van Rossum (home page: http://www.python.org/%7Eguido/)