Earlier quoted context omitted.
Most people will tell you they're using 2.7 in production.
Because of legacy, but these days there is no reason not to use python 3 on new projects. Note that Python 2.x will no longer be supported in 2020.
Well, not that doing so is a bad thing - it's the contrary, esp. if the patch goes to the upstream - but still this may be frustrating to some.
(Most common libraries are actually work pretty well with Python 3. But there are still a lot of stuff PyPI that's Python 2-only at the moment.)