Oh, and when you say there is nothing in the documentation about the 's' case for arbitrary objects, it is made clear in various places that every object has an str, which defaults to its repr if it has no specific __str__.  Combine that with the description of what happens when you use a fixed field length for 's', and you get the results you see.  There should be nothing surprising about this to anyone who has read the tutorial, I think.  (But specific suggestions for improving the docs are always welcome.)