Ran into the first nasty snag: people are abusing os.path.commonprefix() and it's extremely generic approach. Instead of passing in a list of file paths they are passing a list of lists of file path *parts*, e.g. instead of ["a/b", "a/c"] they are passing in [["a", "b"], ["a", "c"]]. I have special-cased when the list contains another list or tuple, but I still feel dirty doing it.