I recommend not going down this path.  The intended purpose of doctest is to test examples in documentation.  In particular, those examples should match what a user would *see* when running the examples.  In essence, the proposal is to allow tests to pass even when the examples *don't* match what the user sees.

ISTM, the str_fun() example *should* fail.  It does not show *any* real interactive prompt session than can be reproduced by a user or anything that a user would ever see.   IMO, that would be a documentation anti-pattern.