I think the benefit of the repr being easier to understand outweighs the pain of breaking the old format. If the change is a problem, that might be mitigated by adding an entry to the “Porting to Python 3.7” documentation.

I don’t think my option of factoring the minus sign out to the front of the timedelta constructor was mentioned on Python-dev. The advantage is that it doesn’t mention problematic negative attribute values, and if you negate a timedelta, you still get the right attribute values:

>>> d
-datetime.timedelta(seconds=60)
>>> -d
datetime.timedelta(seconds=60)
>>> (-d).seconds
60