Abusing a `str()` with new meaning likes this makes no sense at all, if you need a sentinel to indicate this make a new class or a singleton object ``Continue = object()`` to identify this case. Though probably make more sense to either:

- Raise and exception when you can't go forward, analogous to raising `StopIteration`
- Use `None` to indicate the normal action, in the sense "I have no opinion about this, just carry on" and then use ``False`` to indicate not being able to go forward

Though I think I would prefer an exception to trigger the stopping.