major changes with breaking backward compatibility would require a major bump. Fine for python 4 I would say.
[1]: depending on if we count 3.0 vs 3.2 when it was actually kinda usable.
In the doc you linked, they reference "major" and "minor" versions. So they claim to have some concept of version numbers having different significance... Why don't they adhere to semantic versioning if they dress their version numbers like that?
At least Linux just admits their X.Y scheme means nothing.
from __future__ import no_bare_except
I guess that __future__ is doing something similar, but I am thinking of something like declaring how options should be set for your module and then only the code in that module is affected. (It would be nice being able to set constraints on what options your dependencies can enable)
I guess that for std functionality this is impossible (like if the dict changed its key sorting it might be too hard to dispatch on the original file) but for syntax it should be perfectly possible.