The thing that I admire the most about this is how small a change Py3K really is, considering it's the first major compatibility breaking release AFAIK. The change from 1.x to 2.x version numbers was for historical and cosmetic reasons: if you wrote a module in Python 1.5 there's a very good chance you can run it in Python 2.5 with only trivial modifications at worst (e.g., one of your identifiers has become a keyword). This is a testament to the excellent taste of the Python designers, and to their rare mix of restraint and practicality.