> For the next step, I propose to explicitly clear the current exception before raising a new exception.

Attached pyerr_match_clear.patch implements this. It's only a work-in-progress. I prefer to get feedback on the patch before finishing it.

The patch checks also which exception was raised using PyErr_ExceptionMatches() to avoid hiding import exceptions.

Since my patch makes assumption on which exception is expected, it can change the behaviour of functions if I forgot a different exception which is also supposed to be replaced. Example: only catch ValueError and replace it with ValueError, whereas OverflowError must also be replaced with ValueError.