Python does sometimes have backwards-incompatible changes, e.g. for 3.10 they removed a bunch of stdlib modules and methods, like the "formatter" and "parser" module [0].
So if you used those, your code wouldn't work in 3.10.
But the main reason to wait for wheels (which is pythonese for "pre-built packages") is if they use native code (like C or rust) and you would have to compile them yourself otherwise, which increases installation time quite a bit.
(this was also the reason why Alpine was a bad choice for python containers for a long time because it uses musl and there were only wheels for glibc available. AFAIK musl wheels exist now so that isn't relevant anymore)
I always wondered what’s keeping packages back from having wheels ready the day a release drops, or way before even?
I imagine often it’s just another parameter in a CI somewhere, where things mostly “just work” because backward-incompatible breakages have become much rarer.
It's usually a question of having the resources (usually developers to debug issues). IIRC pretty much all Windows wheels are maintained by one guy, Christoph Gohlke, he was a godsend when I worked on a Windows laptop. I owe that guy many beers.
I've never seen a better illustration of xkcd 2347 than Christoph Gohlke. I tried to find a donation link to send him small thank yous but couldn't find one.
Python does sometimes have backwards-incompatible changes, e.g. for 3.10 they removed a bunch of stdlib modules and methods, like the "formatter" and "parser" module [0].
So if you used those, your code wouldn't work in 3.10.
But the main reason to wait for wheels (which is pythonese for "pre-built packages") is if they use native code (like C or rust) and you would have to compile them yourself otherwise, which increases installation time quite a bit.
(this was also the reason why Alpine was a bad choice for python containers for a long time because it uses musl and there were only wheels for glibc available. AFAIK musl wheels exist now so that isn't relevant anymore)
[0]: https://docs.python.org/3/whatsnew/3.10.html#removed