VB6 versus VB.NET is a worse historic pothole of a version change for arguably the same language.
Ultimately the Python 2 -> 3 transition has been as smooth as developers make it. There are certainly a lot of transition efforts put in place, such as the ability to import from __future__ some of the 3 behaviors and abilities and some automated migration tools. At this point, too, most of the major libraries today support 3 and there's few reasons not to build for 3 and maybe do a few tweaks to also support 2, if you truly have to. (A lot of good 3 code runs on 2 unmodified and just needing the Python equivalent of polyfill libraries and __future__ imports.)
Some of the fracture has been binary ABI compatibility and mini-versions of this struggle can certainly be seen in just about any language with an ecosystem of cross-platform native libraries to support (the brief Node/io.js being an interesting fracture more in that it was resolved so amicably so relatively quickly).
But ultimately it's tough to resolve the psychological and political hurdles: for whatever reason there seem to be "die hard" Python 2 fanatics that hate the direction Python 3 has moved and don't seem interested at all in compromise or transition. It certainly doesn't seem to be as strong as the hate divide between VB6 and VB.NET (which will likely forever be a weird blood feud until VBA and VB6 programmers die of old age), but still haters are gonna hate.
Ultimately the Python 2 -> 3 transition has been as smooth as developers make it. There are certainly a lot of transition efforts put in place, such as the ability to import from __future__ some of the 3 behaviors and abilities and some automated migration tools. At this point, too, most of the major libraries today support 3 and there's few reasons not to build for 3 and maybe do a few tweaks to also support 2, if you truly have to. (A lot of good 3 code runs on 2 unmodified and just needing the Python equivalent of polyfill libraries and __future__ imports.)
Some of the fracture has been binary ABI compatibility and mini-versions of this struggle can certainly be seen in just about any language with an ecosystem of cross-platform native libraries to support (the brief Node/io.js being an interesting fracture more in that it was resolved so amicably so relatively quickly).
But ultimately it's tough to resolve the psychological and political hurdles: for whatever reason there seem to be "die hard" Python 2 fanatics that hate the direction Python 3 has moved and don't seem interested at all in compromise or transition. It certainly doesn't seem to be as strong as the hate divide between VB6 and VB.NET (which will likely forever be a weird blood feud until VBA and VB6 programmers die of old age), but still haters are gonna hate.