[ploxiln]

To provide a counter-example: the startup I was working for switched from python-2.7 to python-3.4 after that came out. It was fine, no major issues. I wrote a whole lot of python2.7 before that, and a whole lot of python3.5 afterwards. I maintained our deployment and local dev scripts, and a couple libraries and tools on pypi, which were compatible with both python3 and python2. It was very doable.

I think one mistake was promoting the "2to3" converter early on. It turned out better to add a couple features to python2.7 and python-3.2/3.3/3.4 which made it quite feasible to write code compatible with both.

It is perhaps ironic that writing code that deals with str/unicode/bytes across both python2 and python3 is a bit more complicated than just python2 - but, again, still doable. I did it for years, many popular libraries did it for years, until recently dropping python2 support. It worked.