PyErr_NormalizeException() If a new exception occurs while an exception instance is being created, try harder to make sure there is a traceback. If the original exception had a traceback associated with it and the new exception does not, keep the old exception. Of course, callers to PyErr_NormalizeException() must still be prepared to have tb set to NULL. XXX This isn't an ideal solution, but it's better than no traceback at all. It occurs if, for example, the exception occurs when the call to the constructor fails before any Python code is executed. Guido suggests that it there is Python code that was about to be executed -- but wasn't, say, because it was called with the wrong number of arguments -- then we should point at the first line of the code object anyway.