> I would prefer to use the "same code" (or almost) on all maintained
> versions of Python: 2.7, 3.5, 3.6 and 3.7. It should ease the
> maintenance for bugfixes and enhancements.

This is VERY far from our historical policy for backports.  Python 2.7 is supposed to be getting more stable over time (that is one of its chief virtues).  We don't want to risk the kind of mini-catastrophe that got published in 3.6 (issue29085).  

If you want to push for this, there needs to be a thorough discussion on python-dev (there are tons of possible backports that could be made if the rationale was "I would prefer to use the same code on all maintained versions").