the way to make an (aysnc)generator that immediately raises Stop(Async)Iteration immediately is to insert an unreachable `yield` statement, however there's two ways to do it: def example(): if False: yield or: def example(): return yield currently test_asyncgen.py uses both, eg: @types.coroutine def __anext__(self): if False: yield "this is a generator-based coroutine" if self.yielded >= 2: raise StopAsyncIteration() else: self.yielded += 1 return self.yielded or: async def agenfn(): try: await _async_yield(1) except MyError: await _async_yield(2) return yield the `if False: yield` version has a disadvantage in that it can be anywhere in the function, if this one is chosen then an additional caveat is that it should be the first two statements in a function if `return; yield` version has an disadvantage in that the unreachable yield could be inserted after any `return`, if this one is chosen then an additional caveat is that it should be the last two statements in a function and de-dented as much as syntactically possible. Which alternative do you prefer? I prefer `return; yield`