[muneikh]

partition_all(0, rows) and negative sizes silently produce an empty iterator even with nonempty input. A valid integer-index object is accepted when the iterator group is built, but can raise TypeError later when a short final batch requires arithmetic on the original object.

Normalize the batch size once using operator.index and require it to be positive before touching the source. Document the requirement and test empty/nonempty inputs, unchanged source consumption on invalid size, and an indexable size with a short final batch.

Validation: three regressions fail against the original code; the library and doctest suite passes with the fix (271 passed, 2 skipped). Configured pycodestyle and git diff --check pass. Nonpositive sizes now raise ValueError when the generator is advanced; non-integral sizes remain TypeError.

[carlitogwapito]

An optional test-only commit, based directly on your branch.

Your consumption test checks that the source's values remain available. This adds a guard that raises if __iter__ itself is called, so it also protects sources that initialize work before yielding anything.

Two small checks worth keeping: rejection before source initialization, and both error paths (nonpositive integer sizes and a non-integral size). No real files or network calls are involved.

On Python 3.14.4, all three cases pass your head with zero source starts; the base hits the exact source-start guard. The unchanged normal partition_all test passes on both. Focused Ruff checks pass, and warnings were treated as errors with the existing compatibility-warning exemption. I haven't run the full suite/doctests, configured pycodestyle, package build or version/OS matrix.

To run the added file in your tree: python -m pytest toolz/tests/test_partition_all_preflight.py -q.

[Wkhanex]

Verified 491414b against 504 independently constructed batch expectations: sizes 1–8, source lengths 0–20, and list, tuple and iterator inputs. Each size was a custom __index__ object with a call counter. Every result matched ordinary sequence slicing, including short final batches, and each size was normalized exactly once.

Five invalid-size cases (zero, two negatives, float and string) also left a one-shot source's values untouched. These 1,013 assertions passed on CPython 3.12.14; the base fails on a custom-index size. The four existing partition_all tests pass. This does not add a full-suite or multi-version result.

Review prepared with Codex assistance; the checks described above were executed locally.