[ktz03]

Reference Issues/PRs

No linked issue.

What does this implement/fix? Explain your changes.

Preserve the recorded shape when loading an empty NumPy object array. For example:

import numpy as np
from skops.io import dumps, loads

arr = np.empty((0, 3), dtype=object)
print(loads(dumps(arr)).shape)  # (0,) before; (0, 3) after

Reconstructing the nested list loses dimensions after the first zero-length axis. Allocate empty arrays using the already stored shape; keep nonempty reconstruction, the file format and the trust policy unchanged. Add regression coverage for bytes and file round trips, zero-length axes in different positions, and working empty/nonempty controls.

Validation on Windows CPU with Python 3.12.14, NumPy 2.5.4 and scikit-learn 1.9.1:

• The same 14 new cases fail 6 / pass 8 on the original implementation and all pass after the fix.
• Complete skops/io suite, including doctests, audit and old-protocol tests: 1,108 passed, 66 skipped, 1 existing XPASS. The original implementation has the six failures above; the skips and XPASS remain the same. The skips are optional third-party estimators and one empty parameter set.
• All official pre-commit run --all-files --show-diff-on-failure hooks pass, including Ruff and pyrefly.
• The wheel builds successfully, all 48 packaged Python files match the source, and a separate wheel installation passes the public array/container round-trip checks.

Any other comments?

No protocol bump is needed. The full repository suite, optional external estimators, other operating systems and the official Python/dependency matrix were not tested.

[Copilot]

🟢 Approval recommended

The narrow fix has appropriate regression coverage and no unresolved review findings.

No open issues 🎉

What changed in this PR

Preserves the recorded shape when loading empty NumPy object arrays without changing nonempty reconstruction.

Changes:

• Allocates empty object arrays using their stored shape.
• Adds 14 regression cases covering bytes/file round trips and empty/nonempty controls.
• Documents the fix in the changelog.

File	Description
skops/​io/​tests/​test_persist.py	Adds shape, dtype, and value round-trip checks.
skops/​io/​_numpy.py	Restores empty arrays using the recorded shape.
docs/​changes.rst	Documents preserved empty-array dimensions.

_{Review effort: Balanced}