Apart from the switch from Python 2 to Python 3, I don't recall any Python release, which fundamentally broke backwards compatibility.
I don't think that deprecating Python 2 was the right choice even though a new version has been available for several years. As far as I know you can still compile ANSI C code using the latest version of GCC.
There has been certain practices in how Python programs were invoked, which could lead to accidentally invoking it with a different Python version than intended. With a correct #! line at the top of the program and a correctly installed Python interpreter, that should not happen.
@hyc @nixCraft To be fair, that post is about issues someone is having with selenium, one of the most notoriously fragile third-party Python libraries in existence.
If you want to control a headless browser instead of just making raw http requests, then your code is going to be prone to breakage no matter what language you use.