I don't see any reason why I must do all this extra stuff
You don't have to do all this extra stuff. You could say I'm going with python3 and simply live without (or port or re-implement) any features from third party libraries that don't have a python2 version. Or you could say I'm going with python2 and live with the facts that the language won't be evolving any more and a few years from now most libraries will only see updates to their python3 branch. Both of those approach are also perfectly reasonable depending on the scope of the project.
When there are better alternatives available elsewhere.
Obviously if there are significantly better answers than python to the problem you're facing then you should be using one of those alternatives. I was assuming that you'd already decided that python was the best fit for an upcoming project and needed a plan on how to proceed.
You don't have to do all this extra stuff. You could say I'm going with python3 and simply live without (or port or re-implement) any features from third party libraries that don't have a python2 version. Or you could say I'm going with python2 and live with the facts that the language won't be evolving any more and a few years from now most libraries will only see updates to their python3 branch. Both of those approach are also perfectly reasonable depending on the scope of the project.
When there are better alternatives available elsewhere.
Obviously if there are significantly better answers than python to the problem you're facing then you should be using one of those alternatives. I was assuming that you'd already decided that python was the best fit for an upcoming project and needed a plan on how to proceed.