The syntax between version 2 and 3 of Python are somewhat similar. But there are certain things that are only possible in Python 2 as some libraries are only available on version 2 without porting them across.
I'm not a python user, but I have observed the fact that these two versions have existed in parallel for some time now, obviously one slowly supplanting the other.
Realistically, python is the only language tag here on which this is worth bothering. C++ has undergone a lot of evolution in the last decade, earning it a range of tags on Stack Overflow, and likewise Java versions include nuaces and depreciations, such that it has version specific tags there. These are unlike python in that they try to maintain a very high degree of backward compatibility. Perl, however, is the same in that perl 6 is not backward compatible with 5 or 4 etc. I imagine every language has one distinction or the other with major versions, and there may even be significant differences in the API with minor versions (there are corresponding examples of minor version tagging on S.O., e.g.
lua-5.x). But I do not think it is worthwhile for us here to have multiple perl or C++ or java tags.
So the only serious candidate is python, and what I would suggest, if someone at some point wants to start doing this, is that
python-3 be supplemental and not replacements for
Which then begs the question to what they should be applied, and this is where I'd argue it may be a nuance that's still unnecessary here, since ideally I think they should apply to questions that are specifically and explicitly questions about API differences across versions, which are questions that belong on S.O. period.
However, I might have used
C++11 on S.O. questions without said idealism at work simply because I used some C++11 idiom. I don't know if this is an argument for or against having
My final point about this is it is a basic fact about a language which most users will run across while they are learning the language -- and we are not here to teach people python. There's some expectation that they have a minimal degree of competence in order to be asking a pi specific question. Occasionally it is really clear when someone doesn't (can't use conditionals/loops properly, etc.) and hopefully either those get a quick answer or else they are closed as off-topic. In that context:
Is it worth it to do this just as a friendly heads up?
Is it even effective that way? If I didn't know about it, am I likely to notice because a tag says
python-3, that hey, there's more that one incompatible version of the language in widespread use?
Will it be used enough to make it effective that way?
In short I'm not opposed to new tags (as long as they aren't used to replace
python), but it is not something I would put time into.