> Sure, you can compile and run Python on both versions of Linux, but
> what if your application uses features that are only present in Linux
> 3.0 and later ?

This comment is making me think you've missed just how irrelevant kernel version 3.0 really is. To a first approximation, it *has no new features*. Now, to be sure, there are a couple of things, sure. Just like there were a couple new features in 2.6.39 two months earlier, 2.6.38 two months before that, 2.6.37 two months before that, and so on, every 2-3 months, back to the release of 2.6.7 or so in 2004.

> BTW: The new attribute should contain the complete version number,
> not just the major version. `uname -r` would provide a good start.

To be useful, that would have to be a runtime-computed thing, not the build-time value that sys.platform's trailing number is. But we already have that: os.uname(). It certainly doesn't need a second name.