Rebase range iterator __reduce__ to match CPython - #8424
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range_iterator.__reduce__ (and longrange_iterator) returned the original range plus the current index as pickle state; CPython returns the range rebased to the current position with a None state. Rebase start by index * step (clamped to the length) and emit None. __setstate__ is kept so pickles carrying an integer state still load. Assisted-by: Claude Code:claude-opus-4-8
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ChangesRange iterator reduction
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: ⚪ Minimal · up to This localized compatibility fix changes only how range iterators represent their remaining state during serialization, with round-trip behavior preserved and targeted edge cases covered; no actionable merge-blocking risk remains. Possibly related PRs
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please add a test about this. copying the example code from original issue to extra_tests/snippets/builtin_range.py or stdlib_pickle.py will be good
Assert the rebased range and None state added in the previous commit. The snippet runner executes it under both CPython and RustPython, so it also cross-checks the representation against CPython. Assisted-by: Claude Code:claude-opus-4-8
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Inline comments:
In `@extra_tests/snippets/builtin_range.py`:
- Line 123: In the iterator example containing next(it) calls, split the three
sequential next calls onto separate lines so each line contains one statement
and Ruff E702 is resolved.
- Around line 127-128: Add tests alongside the existing range iterator
assertions for a reversed iterator after exhaustion and after partial
consumption. Verify exhaustion clamps the reduced range appropriately, and
verify consumption rebases the reduced range to the remaining reversed sequence
while preserving the existing assertions and test data.
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extra_tests/snippets/builtin_range.py
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| assert iter(range(3)).__reduce__()[1:] == ((range(0, 3),), None) | ||
| assert reversed(range(3)).__reduce__()[1:] == ((range(2, -1, -1),), None) |
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🎯 Functional Correctness | 🟡 Minor | ⚡ Quick win
Add exhausted and consumed reversed iterator cases.
The current assertions cover unconsumed iterators only. They do not verify exhausted-iterator clamping or rebasing after consuming a reversed iterator. Add both cases.
Proposed test additions
assert iter(range(3)).__reduce__()[1:] == ((range(0, 3),), None)
assert reversed(range(3)).__reduce__()[1:] == ((range(2, -1, -1),), None)
+exhausted = iter(range(3))
+list(exhausted)
+assert exhausted.__reduce__()[1:] == ((range(3, 3),), None)
+
+reversed_it = reversed(range(3))
+next(reversed_it)
+assert reversed_it.__reduce__()[1:] == ((range(1, -1, -1),), None)
+list(reversed_it)
+assert reversed_it.__reduce__()[1:] == ((range(-1, -1, -1),), None)As per coding guidelines, preserve the existing extra-test assertions, logic, and test data. This follows the PR objective to cover rebasing and exhausted-iterator clamping.
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| assert iter(range(3)).__reduce__()[1:] == ((range(0, 3),), None) | |
| assert reversed(range(3)).__reduce__()[1:] == ((range(2, -1, -1),), None) | |
| assert iter(range(3)).__reduce__()[1:] == ((range(0, 3),), None) | |
| assert reversed(range(3)).__reduce__()[1:] == ((range(2, -1, -1),), None) | |
| exhausted = iter(range(3)) | |
| list(exhausted) | |
| assert exhausted.__reduce__()[1:] == ((range(3, 3),), None) | |
| reversed_it = reversed(range(3)) | |
| next(reversed_it) | |
| assert reversed_it.__reduce__()[1:] == ((range(1, -1, -1),), None) | |
| list(reversed_it) | |
| assert reversed_it.__reduce__()[1:] == ((range(-1, -1, -1),), None) |
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In `@extra_tests/snippets/builtin_range.py` around lines 127 - 128, Add tests
alongside the existing range iterator assertions for a reversed iterator after
exhaustion and after partial consumption. Verify exhaustion clamps the reduced
range appropriately, and verify consumption rebases the reduced range to the
remaining reversed sequence while preserving the existing assertions and test
data.
Source: Coding guidelines
Summary
range_iterator.__reduce__(andlongrange_iterator.__reduce__) returned the original range plus the current index as the pickle state, whereas CPython returns the remaining range rebased to the current position with aNonestate. The round-trip result was already correct on both (RustPython restored the index via__setstate__), so this is a representational / cross-compatibility divergence, not data loss.Cause
range_iter_reduceembedded the full original range and passedindexas the third tuple element. BothPyRangeIterator::__reduce__andPyLongRangeIterator::__reduce__go through it.Fix
Rebase the range start by
index * stepand emitNonefor the state. The index is clamped to the length first, because RustPython's iterator increments the index unconditionally, so it can run past the length after exhaustion (unlike CPython, which stops at the length).__setstate__is left intact, so pickles that carry an integer state still load.Test
Verified against CPython 3.14.6 —
__reduce__output now matches for mid-iteration, fresh,reversed, exhausted (range(2, 2)), step > 1, empty, single-element, negative-step,longrange, and__setstate__-advanced iterators.pickle.loads(pickle.dumps(it))round-trips correctly in all cases.test_range: SUCCESS (29 run, 2 skipped — the two skips are a separate, pre-existing__setstate__crash, unrelated to this change).cargo build/cargo clippy -p rustpython-vm/cargo fmt --check: clean.No
@expectedFailuremarker flips here: CPython's owntest_rangehas no test asserting the__reduce__shape, so this is a representational fix, covered for regressions by the existing pickle round-trip tests.Summary by CodeRabbit