A part that bothers me about the PyO3 design is this: does it mean you can't keep Python objects around with the GIL released? e.g. looking at this comment [https://github.com/PyO3/pyo3/issues/55#issuecomment-31728794...] they compare

    impl PyList {
        fn new(py: Python) -> PyList {...}
        fn get_item(&self, py: Python, index: isize) -> PyObject {...}
    }

to

    impl PyList {
       fn new(py: Python) -> &PyList {...}
       fn get_item(&self, index: isize) -> &PyObject {...}
    }

if I don't misunderstand, in rust-cpython (the first snippet) you can have a PyList independent from a Python object (which I understand represents a GIL guard), you just can't operate on it if you don't hold the GIL.

In PyO3 (second snippet) that does not seem to be the case, the object itself has a lifetime dependency on holding the GIL. So you can't e.g. release the GIL to do native processing if you'll still need the native objects afterwards.