Message 230277 - Python tracker

'counter' in the docstrings is in lower case, so that says nothing dispositive.  However, __add__ does an ininstance check, so it is hard to see why __iadd__ does not.

Personally I'd drop the isinstance checks and let the errors bubble up as they may.  Why should subtract explicitly support other data types, but not __sub__/__isub__?  But Raymond's opinion should hold the most weight here.