It depends on what you mean by running unchanged. Numpy and scipy also support 2.4 to 2.7 (and soon to 3.1) from the same codebase. But everytime a new version

It depends on what you mean by running unchanged. Numpy and scipy also support 2.4 to 2.7 (and soon to 3.1) from the same codebase. But everytime a new version of python is out, we need to make some changes, albeit relatively minors. So it is not perfect either.