Antoine: If you're looking at my test.py then my expectation is that this doesn't crash because a RuntimeError should be raised when the maximum recursion limit is hit, and then the trace handler should be uninstalled because it leaks an exception.  And that's exactly what seems to happens on Python 2.x.  We shouldn't ever hit the OS stack limit because Python's recursion limit should be enforced even in the face of a sys.settrace handler.