Whew. Complex issue!

The OP should probably use his workaround or call loop.stop() instead of raising SystemExit.

Asyncio in general is rather careless about "true" BaseExceptions (i.e. that aren't also Exceptions), we should decide what we want to do for these (there are definitely ways to get in a bad state if you catch one and then resume the loop).

call_exception_handler() tries to log and then ignore exceptions raised by the handler, so the except clause Yuri's patch adds to __del__ in fact will only see true BaseExceptions.

Adding an except clause to __del__ seems very unprincipled -- there's another __del__ that would require the same treatment (all our __del__ methods seem to call call_exception_handler()) and *if* we want to catch it we should probably do it in call_exception_handler().

boom() does in fact yield.