Running Python 2 and Python 3 on the same machine

["Martin v. Löwis"]

> Since the source code is incompatible, I was expecting the Python
> executable to have a new name such as 'python3'

It does: the executable is called python3.0.

> or for the default
> source code filename to change to '.py3' or something.

Such a proposal would be rejected. In a few years from now, Python 2
will be gone, and we would be stuck with an ugly file extension
(similar to how \windows\system is now an empty directory, and
\windows\system32 actually contains the 64-bit binaries on x64)-

Regards,
Martin