A python implementation able to run both 3.x and 2.x code would be quite convenient.
PyPy is planning this for the future, but currently it only supports v2.x.
As alternative, is there any wrapper launcher that is able to perform on-the-fly code conversion (like 2to3 and 3to2)?
E.g. for running python3 code on python2 i've written this:
python -c "from __future__ import absolute_import, division, print_function, unicode_literals; execfile(\"$1\");"