Well, twisted always had defer_to_thread. Asyncio has run_in_executor,
but that seems to be callback-based rather than coroutine-based?
The run_in_executor call is not callback-based -- the confusion probably stems from the name of the function argument ('callback'). It actually returns a Future representing the result (or error) of an operation, where the operation is represented by the function argument. So if you have e.g. a function
return 1 if n <= 0 else n*factorial(n-1)
you can run it in an executor from your async(io) code like this:
loop = asyncio.get_event_loop()
result = yield from loop.run_in_executor(factorial, 100)
(In a PEP 492 coroutine substitute await for yield from.)