I would presume most people who are writing 3.x code have written 2.x code before, or don't care about 2.x. I personally have gotten used to the syntax that works in both, and tend to write my code in the most compatible manner possible.
Do you have experience with the `six` library[0]? I've read a few times about it recently and it seems a convenient way to write portable code. I still wait for an opportunity to use it!
[1] https://github.com/twilio/flask-restful/blob/master/flask_re...