OK, fine on the convention, but I'd still like a more memorable name for assert_python_failure.  I've been working on this issue off and on today, and I've had to look up that name at least four times.  I can remember assert_python_ok, but I can't remember whether its inverse is assert_python_fails, assert_python_bad, or what.  For some reason I haven't guessed 'failure' even once so far :)  (I know it's not assert_python_not_ok because I remember it isn't parallel...)