Yeah, I've figured out that rather than exposing __del__ if tp_del is populated, or generalising the generator special case, the simplest way to make this info accessible is to be able to ask the *garbage collector* if it thinks an object needs finalising.

That actually makes this a pretty easy issue (as C issues go) - it's just a matter of exposing http://hg.python.org/cpython/file/default/Modules/gcmodule.c#l525 (has_finalizer) as gc.needs_finalizing.

It will be easier once #17468 is done though, since that will make it clearer what the documentation should say.