> and require the Python 3 interpreter to be able to interpret Python 2 code as well as Python 3 code?
The interpreter is too messy for that and the transition to Python 3 was not considered well enough. There is no hope on that front. Even if you solve everything else, the C ABI will still be broken.
The interpreter is too messy for that and the transition to Python 3 was not considered well enough. There is no hope on that front. Even if you solve everything else, the C ABI will still be broken.