[wycats]

The primary difference between Ruby and Python, from where I'm sitting, is that Ruby's change was purely at the API level, so it was feature-detectable and shimmable by libraries like Rails. I talk elsewhere in this thread about the effort we had to do, but the point is, we could do it.

In contrast, Python 3 changed the meaning of "foo". It also supported only u"foo" in Python 2 (to opt-in to unicode strings) and only b"foo" in Python 3 (to opt-in to byte-strings) for a fairly long period of time, making it extremely, extremely awkward (at best) to write a program with shims as abstractions that let most of the program remain oblivious to the differences.

Python 3.3 and 2.7 finally landed a lot of fixes to this kind of problem, but it landed fairly late, and after most of the community got a sense of the relative difficulty level of a transition to Python 3 that maintained support for Python 2 at the same time.

Both Ruby and JavaScript have taught me the value of a transition path to a new version that allows people to write libraries that support both the old and new version at the same time. Communities move a little at a time, especially long-term production projects. The best way to move them is via libraries that can serve as a bridge and target both the old and new version together.