Comparing with Python 1.* - 2.*

My feeling is that the move to Python 3 has pretty much the same life-cycle as the move from Python 1.5/6 to Python 2.0. It took a bit of time to move all the modules over to the new world, and there was no clear "flag day", but now it's incredibly rare to see a 1.5-only module.

The argument against this is that the Python ecosystem is now far larger and mature to manage a similar transition, but honestly I think that is overstating Python's presence in the world for now. It's still growing, but the number of libraries and interdependencies is really not as great as, say, C++ or even Perl. I think in 6 years, python 2.0 will be as historical an oddity as Perl 4 (and Python will still be around, I hope).