[Python] Fix UUID extension type round-trip to pandas returning bytes natively - #55
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[Python] Fix UUID extension type round-trip to pandas returning bytes natively#55rok wants to merge 2 commits into
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Aug 18, 2026
…ning bytes (#50325) ### Rationale for this change Converting a Table with an `arrow.uuid` extension column to pandas currently produces a column of `bytes` instead of `uuid.UUID` objects. Without a dedicated conversion path, `Table.to_pandas()` / `Array.to_pandas()` falls back to the storage type (`fixed_size_binary(16)`) and materializes raw bytes. Downstream callers (and tests such as those landing via pandas UUID Parquet coverage) expect `uuid.UUID` objects, matching what `to_pylist()` / `UuidScalar.as_py()` already return. Note: the original issue suggested this might be specific to Python 3.14, but the same `bytes` result reproduces on Python 3.10-3.14 with current PyArrow - `UuidType` never had a pandas conversion path. Closes#50312 ### What changes are included in this PR? Convert UUID extension arrays to `uuid.UUID` objects in the C++ pandas conversion path (integrated from @ rok's proposal in rok#55), rather than relying on a Python `to_pandas_dtype()` / `__from_arrow__` compat layer: - Construct `uuid.UUID` objects from storage bytes in `helpers.cc` (`UuidFromBytes`) and use that from `arrow_to_pandas.cc` - Reuse empty kwargs / shared empty tuple constants so conversion does not allocate per element - Keep `to_numpy(zero_copy_only=False)` on UUID extension arrays returning storage `bytes` (extension to NumPy should follow storage type) - Add/extend regression tests for pandas round-trip and NumPy behavior ### Are these changes tested? Yes. Acceptance criteria: - [x] Tests added for the UUID to pandas round-trip (and NumPy storage behavior) - [x] Relevant local / CI Python tests passing for the touched paths - [x] Follows project style / review feedback (lint fix included) - [x] No intentional breaking public API change beyond correcting incorrect `bytes` return values to `uuid.UUID` for `to_pandas()` Before / after evidence (backend; console): ```text # Before (repro on Python 3.10-3.14 with unfixed PyArrow) >>> type(result_df.loc[0, "id"]) <class 'bytes'> # After (with this PR) >>> type(result_df.loc[0, "id"]) <class 'uuid.UUID'> ``` Also covered by added unit tests in `python/pyarrow/tests/parquet/test_data_types.py` and `python/pyarrow/tests/test_extension_type.py`. ### Are there any user-facing changes? Yes. `Table.to_pandas()` / `Array.to_pandas()` now returns `uuid.UUID` for `arrow.uuid` columns instead of `bytes`. `to_numpy(zero_copy_only=False)` continues to expose storage `bytes`. * GitHub Issue: #50312 Authored-by: parker-cassar <parker.cassar@berkeley.edu> Signed-off-by: Rok Mihevc <rok@mihevc.org>
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This is to discuss perhaps changing approach on apache#50325