Welcome to the wired world of ironpython and perhaps jython. Strings/Unicode/Bytes are 3.x, standard lib is 2.x.
I think I am slowly growing a courage to make 3.x addition to the ironpython modules.
For things which have different signute (e.g. socket.send) it is trivial, for things where only return value differs, I will very likely add extra method - encode would have encode3. For the second I still need ifdefs in application code.
As long as it doesn't break existing codebase I have a chance to get it into 2.7 maintenance