> They did this by not breaking the universe in these major updates
I don't think the amount of breakage per se was the problem with Python 3. I think the problem was that for a long time (until u"" strings in 3.3? four years after 3.0?) there was ~no way for a library to support both 2 and 3 in a single codebase. That meant that each project had to either maintain a fork, or do a "flag day" migration, which in practice meant you couldn't migrate until all your dependencies were migrated. Big mistake in retrospect.
I don't think the amount of breakage per se was the problem with Python 3. I think the problem was that for a long time (until u"" strings in 3.3? four years after 3.0?) there was ~no way for a library to support both 2 and 3 in a single codebase. That meant that each project had to either maintain a fork, or do a "flag day" migration, which in practice meant you couldn't migrate until all your dependencies were migrated. Big mistake in retrospect.