FWIW I think the octint class is a great idea.  It's nice and localized, and it should have no performance impact and only a small maintenance impact.  It'll also preserve the readability of the default if you pull it out with inspect.getfullargspec / inspect.Signature and repr it.  I'm not sure how IDLE et all produce their tooltips, but whatever technique they use octint should work there.  Heck, it should even survive calculations for default values (as I mentioned in the original post), assuming that int + octint = octint.

Is there a significant downside to octint that I'm missing?