Well, the problem with both [:-1] and os.path.join is that they are inappropriate for that section of the tutorial.  I considered putting the discussion later in the section so that I could use [:-1] (which hasn't been introduced at that point), but it made the flow even worse than adding the text where I did.  I suppose the os.path.join could be put in if the sentence was short and cross referenced the library docs rather than going into a detailed example.