> Would your decision be more favorable if you received a patch implementing this feature?

I'll keep this on "pending" for other devs to weigh in with opinions.

In general, we are not keen on keeping text representations stable, as they do not form part of the API.  This is true for exception messages most of all, but also the representations of other types change occasionally.  Doctests and other test methods that rely on exact output, such as yours, have to adapt to that.

The patch wouldn't be difficult to write, but the issue is more that it isn't really generally useful (as evidenced by the fact that you are the first to request it), and it won't save you a lot of work in any case if you want to support existing versions of Python (2.7, 3.x) as well: the new feature could only go into 3.5.