gh-92154: Expose PyCode_GetCode in the C API

[Fidget-Spinner]

Fixes#92154.

[Fidget-Spinner]

I forgot if this or a TypeError is preferred for the C API (or no error setting at all?)

[markshannon]

Use PyCode_GetCode(PyCodeObject *co) and then you won't need the check.

[Fidget-Spinner]

I would like to, but co_code was previously PyObject*, and I want this to be a drop-in replacement as far as possible.

[vstinner]

PyErr_BadInternalCall() is fine, but I would even suggest replacing a runtime check with an assertion. The caller is responsible to pass the right type.

[Fidget-Spinner]

Also I frankly have no clue if we need to update stable_abi.toml. I'm not sure when it counts as stable ABI and when it doesn't.

[vstinner]

PyErr_BadInternalCall() is fine, but I would even suggest replacing a runtime check with an assertion. The caller is responsible to pass the right type.

[vstinner]

Also I frankly have no clue if we need to update stable_abi.toml. I'm not sure when it counts as stable ABI and when it doesn't.

Include/cpython/ is the API excluded from the limited C API and so excluded from the stable ABI: https://devguide.python.org/c-api/

Please don't add this function to the stable ABI yet. Let's wait for one Python release, and then see if it's stable or not.

[vstinner]

I prepared PR python/pythoncapi-compat#34 to add the function to pythoncapi-compat.

[vstinner]

LGTM.