GH-47823: [Python] Use PyWeakref_GetRef instead of PyWeakref_GET_OBJECT (Python 3.15)

[paultiq]

Rationale for this change

pyarrow builds fail on CPython 3.15 due to the 3.15's removal of PyWeakref_GetObject, used in extension_types.cc. This was deprecated in 3.13. A backport is available in the already-vendored pythoncapi_compat.

Fixes #47823. To be clear: this fixes only the build issue reported in the issue, not "3.15 support".

What changes are included in this PR?

Replaces the sole use of PyWeakref_GET_OBJECT with the backported version of PyWeakref_GetRef.

This follows the recommendation from Pending removal in Python 3.15

PyWeakref_GetObject() and PyWeakref_GET_OBJECT(): Use PyWeakref_GetRef() instead. The pythoncapi-compat project can be used to get PyWeakref_GetRef() on Python 3.12 and older.

Are these changes tested?

Build and tested on a local Ubuntu 24.04 build.

Are there any user-facing changes?

No user-facing changes.

• GitHub Issue: [Python][C++] Python 3.15 Builds Fail due to PyWeakref_GET_OBJECT Removal #47823

[github-actions]

⚠️ GitHub issue #47823 has been automatically assigned in GitHub to PR creator.

[raulcd]

@github-actions crossbow submit -g python -g wheel

[github-actions]

Revision: 563a421

Submitted crossbow builds: ursacomputing/crossbow @ actions-4a1a654c08

Task	Status
example-python-minimal-build-fedora-conda
example-python-minimal-build-ubuntu-venv
python-sdist
test-conda-python-3.10
test-conda-python-3.10-hdfs-2.9.2
test-conda-python-3.10-hdfs-3.2.1
test-conda-python-3.10-pandas-1.3.4-numpy-1.21.2
test-conda-python-3.11
test-conda-python-3.11-dask-latest
test-conda-python-3.11-dask-upstream_devel
test-conda-python-3.11-hypothesis
test-conda-python-3.11-pandas-latest-numpy-latest
test-conda-python-3.11-spark-master
test-conda-python-3.12
test-conda-python-3.12-cpython-debug
test-conda-python-3.12-pandas-latest-numpy-1.26
test-conda-python-3.12-pandas-latest-numpy-latest
test-conda-python-3.13
test-conda-python-3.13-pandas-nightly-numpy-nightly
test-conda-python-3.13-pandas-upstream_devel-numpy-nightly
test-conda-python-3.14
test-conda-python-emscripten
test-cuda-python-ubuntu-22.04-cuda-11.7.1
test-debian-12-python-3-amd64
test-debian-12-python-3-i386
test-fedora-42-python-3
test-ubuntu-22.04-python-3
test-ubuntu-22.04-python-313-freethreading
test-ubuntu-24.04-python-3
wheel-macos-monterey-cp310-cp310-amd64
wheel-macos-monterey-cp310-cp310-arm64
wheel-macos-monterey-cp311-cp311-amd64
wheel-macos-monterey-cp311-cp311-arm64
wheel-macos-monterey-cp312-cp312-amd64
wheel-macos-monterey-cp312-cp312-arm64
wheel-macos-monterey-cp313-cp313-amd64
wheel-macos-monterey-cp313-cp313-arm64
wheel-macos-monterey-cp313-cp313t-amd64
wheel-macos-monterey-cp313-cp313t-arm64
wheel-macos-monterey-cp314-cp314-amd64
wheel-macos-monterey-cp314-cp314-arm64
wheel-macos-monterey-cp314-cp314t-amd64
wheel-macos-monterey-cp314-cp314t-arm64
wheel-manylinux-2-28-cp310-cp310-amd64
wheel-manylinux-2-28-cp310-cp310-arm64
wheel-manylinux-2-28-cp311-cp311-amd64
wheel-manylinux-2-28-cp311-cp311-arm64
wheel-manylinux-2-28-cp312-cp312-amd64
wheel-manylinux-2-28-cp312-cp312-arm64
wheel-manylinux-2-28-cp313-cp313-amd64
wheel-manylinux-2-28-cp313-cp313-arm64
wheel-manylinux-2-28-cp313-cp313t-amd64
wheel-manylinux-2-28-cp313-cp313t-arm64
wheel-manylinux-2-28-cp314-cp314-amd64
wheel-manylinux-2-28-cp314-cp314-arm64
wheel-manylinux-2-28-cp314-cp314t-amd64
wheel-manylinux-2-28-cp314-cp314t-arm64
wheel-musllinux-1-2-cp310-cp310-amd64
wheel-musllinux-1-2-cp310-cp310-arm64
wheel-musllinux-1-2-cp311-cp311-amd64
wheel-musllinux-1-2-cp311-cp311-arm64
wheel-musllinux-1-2-cp312-cp312-amd64
wheel-musllinux-1-2-cp312-cp312-arm64
wheel-musllinux-1-2-cp313-cp313-amd64
wheel-musllinux-1-2-cp313-cp313-arm64
wheel-musllinux-1-2-cp313-cp313t-amd64
wheel-musllinux-1-2-cp313-cp313t-arm64
wheel-musllinux-1-2-cp314-cp314-amd64
wheel-musllinux-1-2-cp314-cp314-arm64
wheel-musllinux-1-2-cp314-cp314t-amd64
wheel-musllinux-1-2-cp314-cp314t-arm64
wheel-windows-cp310-cp310-amd64
wheel-windows-cp311-cp311-amd64
wheel-windows-cp312-cp312-amd64
wheel-windows-cp313-cp313-amd64
wheel-windows-cp313-cp313t-amd64
wheel-windows-cp314-cp314-amd64
wheel-windows-cp314-cp314t-amd64

[raulcd]

This LGTM, @rok @AlenkaF @pitrou do you want to take a look?

[AlenkaF]

LGTM, the change from PyWeakref_GET_OBJECT to PyWeakref_GetRef is clear. Thanks for the contribution!