My Python IDE of choice, Wing, has a capability to start the debugger when an exception is raised, but only if it “appears unhandled”. It’s great but a little delicate. It broke entirely on my recently, all exceptions appeared unhandled. I narrowed the problem down to running in Python 2.7.1. Python 2.6 works fine. The workaround Wing recommended was setting the debugger to break when exception is printed.