Allow reflected fallback for in-place set operators by 1ndahous3 · Pull Request #9182 · RustPython/RustPython

1ndahous3 · 2026-10-17T22:51:57Z

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Found while constructing a parser with Lark, where set |= OrderedSet raised TypeError instead of calling the reflected operator.

Summary

Return NotImplemented from set's |=, &=, -=, and ^= operators for unsupported right operands, allowing their reflected operators to run.

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Bug Fixes
- In-place set union, intersection, subtraction, and symmetric difference now handle dictionary key views correctly, producing the expected set without changing the original set.

Assisted-by: Codex:gpt-6

chatgpt-codex-connector · 2026-10-17T22:52:06Z

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📝 Code Review	✅ Completed 2026-10-17T22:54:53.312873Z	`860ea6e`	PR opened

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coderabbitai · 2026-10-17T22:52:35Z

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📒 Files selected for processing: 2

crates/vm/src/builtins/set.rs
extra_tests/snippets/builtin_set.py

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📝 Walkthrough

The four in-place set operators now return NotImplemented for right operands that are not sets or frozensets. Tests cover direct operator-method results and operations with a dictionary keys view.

Changes: Set In-Place Operator Dispatch

Layer / File(s)	Summary
Operand checks and tests `crates/vm/src/builtins/set.rs`, `extra_tests/snippets/builtin_set.py`	The subtraction, intersection, symmetric-difference, and union slots now check that the right operand is a set or frozenset. Tests expect each direct method to return `NotImplemented` for a dictionary keys view and check the corresponding `operator` result and source set.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: youknowone

Merge Risk: ⚪ Minimal · up to 860ea

No merge-blocking issue is identified; the change is ready for normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the main change: unsupported right operands now allow reflected fallback for in-place set operators.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Reviewed commit: 860ea6e3c7

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youknowone · 2026-10-18T02:04:20Z

            }),
            inplace_subtract: Some(|a, b, vm| {
-                if let Some(a) = a.downcast_ref::<PySet>() {
+                if let Some(a) = a.downcast_ref::<PySet>()


is there any case PySet but not PyAnySet?

the left operand needs to remain a PySet because these slots call mutating PySet::__i*__ methods. PyAnySet would also accept frozenset, which cannot be modified in place. Augmented assignment on a frozenset uses the regular binary operation and reassigns the result instead.

the right operand is only read, so accepting PyAnySet there is appropriate.

I am still not getting how it concludes to add PyAnySet check.
if a is downcasted PySet, It can't be a frozenset. isn't it?
What's the role of the PyAnySet check?

the condition now checks each operand separately:

a (left-hand operand): PySet — this check already existed before this PR. These slots mutate the left operand, so it must be a mutable set. You’re right that a successful downcast already excludes frozenset.

b (right-hand operand): PyAnySet — this check is added by this PR. The in-place methods accept either set or frozenset here. For other types, such as dict_keys, the slot should return NotImplemented. Previously, try_from_object(...)? raised TypeError immediately, preventing normal binary dispatch from reaching the right operand’s reflected method, such as __ror__.

oh, you are right. I was watching b as a and very confused 🤦
Thank you for clearly pointing it out!

Allow reflected fallback for in-place set operators

860ea6e

Assisted-by: Codex:gpt-6

chatgpt-codex-connector Bot reviewed Oct 17, 2026

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Comment thread extra_tests/snippets/builtin_set.py

youknowone reviewed Oct 18, 2026

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youknowone approved these changes Oct 18, 2026

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youknowone merged commit e7e3dfd into RustPython:main Oct 18, 2026
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1ndahous3 deleted the set_inplace_reflected branch October 19, 2026 11:46

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Allow reflected fallback for in-place set operators - #9182

Allow reflected fallback for in-place set operators#9182
youknowone merged 1 commit into
RustPython:mainfrom
1ndahous3:set_inplace_reflected

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