One final note: changing the `main()` function from the example to add a zero-sleep seems to fix it, but this seems like a rather ad-hoc solution.

```
async def main():
    async for i in double(count()):
        if i > 10:
            break
        print(i)
    await asyncio.sleep(0)
```

result:

```
$ python example.py 
0
2
4
6
8
10
double() cleanup
count() cleanup
```