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 it actually is fun to use Python again. The rest of this post explains my conclusion in great detail. My hope is that it will be useful to other Python projects to provide tips and examples how to support both Python 2 and 3, as well as to future language designers to keep languages backwards compatible.
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