[C-API] Add a function to access PyCodeObject.co_code in C

[Fidget-Spinner]

Feature or enhancement

Previously, you could access the co_code field in PyCodeObject directly to access the bytecode. This is no longer the case since 2bde682. Currently in 3.11a7+, C code cannot easily obtain the equivalent of co_code in 3.10. co_code_adaptive gets quickened bytecode which is not equivalent to the 3.10 behavior.

I would imagine many tools relying on the old behavior will break.

Pitch

I propose we expose some form of the currently internal _PyCode_GetCode.

Previous discussion

Related to #91397.
See also coverage.py issue coveragepy/coveragepy#1367

CC @vstinner @nedbat @brandtbucher @markshannon

[vstinner]

See also #91397 "[C API] Move the PyCodeObject structure to the internal C API (make the structure opaque)".

[vstinner]

Even if no function is added, please document at least the member removal in https://docs.python.org/dev/whatsnew/3.11.html (C API > Porting to Python 3.11) since the PyCodeObject structure is part of the public C API.

[markshannon]

Exposing PyCode_GetCode makes sense to me, as it equivalent to code.co_code.

@brandtbucher

[brandtbucher]

Sounds good to me as well.

[vstinner]

And I added the function to pythoncapi-compat: python/pythoncapi-compat@85d1bd8