I'll start with the conclusion: making backwards incompatible version of a language is a terrible idea, and it was bad a mistake. This mistake was somewhat corrected over the years by eventually adding features to both Python 2.7 and 3.3 that actually allow to run a single code base on both Python versions --- which, as I show below, was discouraged by both Guido and the official Python documents (though the latest docs mention it)... Nevertheless, a single code base fixes pretty much all the problems and i
When Python 3.x got released, it was pretty much a new language, backwards incompatible with Python 2.x, as it was not possible to run the same source code in both versions. I was extremely unhappy about this situation, because I simply didn't have time to port all my Python code to a new language.
I read the official documentation about how the transition should be done, quoting: