Elvis, I agree that the masking is not nice. To call it a tracker bug (as opposed to design bug), you need to show that the behavior is different from what is documented. Of course, This issue illustrates why one should have unit tests that try to test each component as directly as possible.

>A certain amount of exception masking is inherent is Python's design. 

This issue comes up in other contexts, such as attribute access.

 >We use TypeError for a lot of things, including the exception raised by "len(obj)" when obj doesn't have length.

Using user-level Exceptions internally is convenient, but possibly a small design flaw. Leaving code breakage aside, would it be possible to define private, undocumented inaccessible-from-Python-code internal subclasses such as _TypeError that never show up in Python level tracebacks (absent extension errors)?