Yeah, the "transparent exception chaining" code falls into the category of code that I'm both proud of (since it works really well in typical cases [1]) and somewhat horrified by (since the *way* it works tramples over several principles of good object oriented design and is completely non-portable to other Python implementations).

Anyway, I've adjusted the issue title here to indicate that we don't want to remove the exception wrapping entirely, just make it less intrusive.

[1] See the hex encoding and bz2 decoding failure examples in https://docs.python.org/3/whatsnew/3.4.html#codec-handling-improvements