It seems we might want a helper method like

```
def render_response_if_needed(self, request, response):
   if not request.finished:
       if response and response is not NOT_DONE_YET:
           request.write(response)
```

I am still not sure when you'd have a _render_after method that would be unaware of the response.  Or a render_before method that would be unaware of the response.