Living through it... Python 3 made a lot of changes for the better but 3.0 in particular included a bunch of unforced errors that made it too hard for people to upgrade in one go.

It wasn't until much later (I would say 3.4 or 3.5?) that we had good tooling to allow for migrating from Python 2 to Python 3 gradually, which is what most tools needed to do.

The final thing that made Python upgrading easy was making a bunch of changes (along with stuff like six) so that you could write code that would run identically in Python 2 and Python 3. That lets you do refactors over time, little cleanups, and not have the huge "move to Python 3" commit.

> Python is by most measures the most popular language and became so AFTER that switch

The switch had nothing to do with Python's rise in popularity though, it was because of NumPy and later PyTorch being adopted by data scientist and later machine learning tasks that themselves became very popular. Python's popularity rose alongside those.

> There is no reason for anyone to be complaining about it being too hard to upgrade in 2026

The "complaints" are about unnecessary and pointless breakage, that was very difficult for many codebases to upgrade for years. That by now most of these codebases have been either abandoned, upgraded or decided to stick with Python2 until the end of time doesn't mean these pains didn't happen nor that the language's developers inflicting them to their users were a good idea because some largely unrelated external factors made the language popular several years later.

It took a long time for python 3 to add the necessary backwards compatibility features to allow people to switch over. Once they did it was fine, but it was a massive fuck up until then. The migration took far longer than it should have done

Its widely regarded as a disaster for good reason, that forced some corrections in python to fix it. Just because its fine now, does not mean it was always fine

Those are unrelated.