GH-46355: [Python] Fix table.to_struct_array with an empty table

[hombit]

Rationale for this change

Currently pyarrow.Table.to_struct_array fails if table is empty, this PR fixes that. See issue #46355 for the reproducible example.

What changes are included in this PR?

Check if table is empty and create an empty chunked array using table schema for the array type

Are these changes tested?

I added a test for that, it failed before I implemented the fix

Are there any user-facing changes?

No

• GitHub Issue: [Python] table.to_struct_array fails for empty table #46355

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

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Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

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See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #46355 has been automatically assigned in GitHub to PR creator.

[hombit]

@AlenkaF @raulcd @rok it is ready now, could you please review it?

[raulcd]

Thanks for the PR. The fix sounds reasonable to me but I would like for @AlenkaF and/or @rok to take a look!

[AlenkaF]

@github-actions crossbow submit -g python

[github-actions]

Revision: 03f330d

Submitted crossbow builds: ursacomputing/crossbow @ actions-39637f523f

Task	Status
example-python-minimal-build-fedora-conda
example-python-minimal-build-ubuntu-venv
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-latest-numpy-latest
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-1.26
test-conda-python-3.11-pandas-latest-numpy-latest
test-conda-python-3.11-pandas-nightly-numpy-nightly
test-conda-python-3.11-pandas-upstream_devel-numpy-nightly
test-conda-python-3.11-spark-master
test-conda-python-3.12
test-conda-python-3.12-cpython-debug
test-conda-python-3.13
test-conda-python-3.9
test-conda-python-3.9-pandas-1.1.3-numpy-1.19.5
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-39-python-3
test-ubuntu-22.04-python-3
test-ubuntu-22.04-python-313-freethreading
test-ubuntu-24.04-python-3

[AlenkaF]

Looks good to me too, thanks! 👍
I have run Python extended builds, just in case. Lets wait for them to finish before merging.

[raulcd]

The CI failures are unrelated.
The minimal examples fail because the fork repository does not have the development tags. This is a known issue:

• [Python] Jobs fail if Pyarrow version is not correctly generated due to missing remote dev tags #44803

The Python 3.10 are related to the test_gdb.py issue:

• [CI][Python] Conda Python 3.10 jobs fail with UnicodeDecodeError due to gdb issue #46343

[conbench-apache-arrow]

After merging your PR, Conbench analyzed the 4 benchmarking runs that have been run so far on merge-commit 88815a1.

There were no benchmark performance regressions. 🎉

The full Conbench report has more details.