Python 2.6 has from __future__ import print_function.
There the saving of implementation effort would be not supporting print statements in 3.0.
Nice it actually gives "SyntaxError: invalid syntax", but then it affects all the imported libraries so I still prefer the per-file way as a transition.
__future__ imports are per file. A few posts up you were proposing an interpreter-wide switch. Did you change your mind?
Awesome. I think both are great, first doing file-per-file and once it's working switching the global switch is a pretty good transition workflow.