Claude/py312 modernizations

[d-v-b]

I had claude do a review of our test suite. The tracking issue is on my fork of zarr-python.

Summary

Addresses M1–M5 of #181. Replaces Python <3.12 patterns with stdlib equivalents now that the minimum Python version is 3.12. Behavior is identical; no public API changes.

M1 — itertools.batched (codec_pipeline.py)

• Deleted the hand-rolled batched() generator and the islice import it depended on.
• Added batched to the existing from itertools import line.
• No external callers import batched from this module (verified with grep across src/ and tests/).

M2 — collections.abc.Buffer (codecs/crc32c_.py)

• Removed import typing_extensions.
• Added from collections.abc import Buffer as ABCBuffer (stdlib since 3.12).
• Replaced both cast("typing_extensions.Buffer", ...) calls with cast(ABCBuffer, ...).

M3 — Remove unused ParamSpec / P (core/sync.py)

• Removed from typing_extensions import ParamSpec and the unused P = ParamSpec("P") assignment.
• Verified with grep that nothing imports P from zarr.core.sync.

M4 — math.prod for integer products

• common.py: Rewrote product() body as return math.prod(tup); removed the now-unused import functools and import operator. The name product is preserved because it is imported in src/zarr/codecs/numcodecs/_codecs.py, src/zarr/core/indexing.py, and tests/test_codecs/test_codecs.py.
• indexing.py (~line 1190): Replaced reduce(operator.mul, cdata_shape, 1) with math.prod(cdata_shape); removed unused import operator and reduce from the functools import.
• array.py (AsyncArray.size ~line 908): Replaced np.prod(self.metadata.shape).item() with math.prod(self.metadata.shape). self.metadata.shape is tuple[int, ...]. Added import math.
• chunk_grids.py (~line 855, _guess_num_chunks_per_axis_shard): Replaced np.prod(chunk_shape) with math.prod(chunk_shape). chunk_shape is typed tuple[int, ...]. math already imported.
• chunk_grids.py lines 689, 704, 711 SKIPPED: These operate on chunks = np.maximum(np.array(shape, dtype="=f8"), 1) — a numpy float64 array. Converting to math.prod would be incorrect (it expects an iterable of numbers and the semantics differ for floating-point arrays). Left unchanged.
• numcodecs/_codecs.py ~21 SKIPPED: Line 21 is inside a docstring code example (np.arange(np.prod(array.shape),...)), not executable source. The actual production usage in that file already calls product() from zarr.core.common (line 264) and is unchanged.

M5 — pathlib in _local.py (~lines 366, 372)

• os.path.exists(dest_root) → dest_root.exists() (dest_root is a Path).
• os.path.getsize(self.root / key) → (self.root / key).stat().st_size.
• import os retained — still used for os.makedirs, os.rename, os.link, os.unlink.

Test results

uv run pytest tests/test_codecs/test_codecs.py tests/test_store/ tests/test_indexing.py tests/test_common.py tests/test_codec_pipeline.py -q
1410 passed, 182 skipped, 5 xfailed in 51.00s

uv run pytest tests/test_codecs/test_crc32c.py tests/test_array.py tests/test_chunk_grids.py -q
1379 passed, 31 skipped in 9.59s

uv run mypy src/zarr/core/codec_pipeline.py src/zarr/codecs/crc32c_.py src/zarr/core/sync.py src/zarr/core/common.py src/zarr/core/indexing.py src/zarr/core/array.py src/zarr/core/chunk_grids.py src/zarr/codecs/numcodecs/_codecs.py src/zarr/storage/_local.py
Success: no issues found in 9 source files

Notes

• A towncrier changelog entry should be added before un-drafting this PR.
• All pre-commit hooks (ruff check, ruff format, mypy, codespell, numpydoc-validation, sp-repo-review) pass.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.47%. Comparing base (4e79f1b) to head (c67b316).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4087   +/-   ##
=======================================
  Coverage   93.47%   93.47%           
=======================================
  Files          90       90           
  Lines       11967    11958    -9     
=======================================
- Hits        11186    11178    -8     
+ Misses        781      780    -1     

Files with missing lines	Coverage Δ
src/zarr/codecs/crc32c_.py	97.22% <100.00%> (ø)
src/zarr/core/array.py	97.87% <100.00%> (+<0.01%)	⬆️
src/zarr/core/chunk_grids.py	96.94% <100.00%> (ø)
src/zarr/core/codec_pipeline.py	95.28% <100.00%> (+0.25%)	⬆️
src/zarr/core/common.py	88.69% <100.00%> (-0.14%)	⬇️
src/zarr/core/indexing.py	96.29% <100.00%> (ø)
src/zarr/core/sync.py	94.23% <ø> (-0.11%)	⬇️
src/zarr/storage/_local.py	95.04% <100.00%> (ø)

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[d-v-b]

these are minor changes and reverting this PR would be very cheap. I am using an agent to review, and I will self-merge if nothing turns up