[geofft]

I'm not deeply familiar with the CPython API, but that should be completely straightforward as long as you don't trade native CPython structures between interpreters. If you start with something like Numpy's array interface, and implement an array in C that knows that it could be accessed by multiple Python interpreters and needs to become immutable before it's passed, it should work. But I wouldn't expect it to be easy to take a regular PyObject and move it between interpreters, so the cost of serialization and deserialization might be an issue.