[CJefferson]

The reason you would assume it is that, for a long time on every Linux distribution, there was a single way to run python2, and it was called 'python'. I'm not sure what you are getting at, this was just the way it was. You couldn't run python 2 any other way in some linux distros.

The reason we don't need a 'bash4' is that, by and large, bash tried very hard to make sure they didn't break any bash3 scripts, so there is no need for old bash3 scripts to know they are now running in bash4, unlike python3.

[michrassena]

I get the point, python 2 scripts aren't fully compatible with python 3. I've written a little python and know that to be the case.

However, I can predict with near certaintly, if python 4 doesn't break python 3 scripts, people will complain if "python3" doesn't invoke python 4, because they've always used "python3" to run the new python and "python" to run python 2.