Thank you Nick for the comments! Updated patch attached.

The new patch uses inspect.stack() to calculate the total stack size, but I'm unable to get the exact number needed, and I found that I'm either 19 or 20 above (depending on whether I run it with -m or manually). The test now "just works" with it, but I'm quite sure it's going to break at some point. Any idea?

The other alternative would be to use traceback.walk_tb(exc.__traceback__), but the Python implementation uses that, so it'd be comparing itself; and that's about as useful as not caring about the size at all. (On the other hand, the C and Python implementations get the exact same number, so it can confirm it's fine)