Guido> Maybe these lines in test_dis.py? ... Skip> Thanks, I'll take a look. I was expecting there'd be a standalone Skip> script somewhere. Hadn't considered that comments would be hiding Skip> code. Indeed, that did the trick, however... I'm a bit uncomfortable with the methodology. It seems test_dis is using the same method (dis.get_instructions) to both generate the expected output and verify that dis.get_instructions works as expected. For the most part, you see the test case fails, rerun the code to generate the list, substitute, et voila! The test (magically) passes. Somewhere along the way, it seems there should be a way to alert the user that perhaps dis.get_instructions is broken and its output is not to be trusted completely. Skip