Reuse stored hashes in set operations and fix key comparison order by 1ndahous3 · Pull Request #8852 · RustPython/RustPython

1ndahous3 · 2026-09-27T08:37:30Z

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Summary

Reuse stored hashes in set/frozenset comparisons and predicates, avoiding temporary sets for native subset checks.
Intersect native sets using the smaller operand without first copying the left operand; preserve the corresponding equal key and subclass iterator behavior.
Hash each generic intersection element once and stop intersection/subset iteration after all source elements match. Dictionary arguments use generic iteration and hashing, matching CPython.
Compare stored dictionary/set keys before lookup keys, preserving NotImplemented fallback and subclass comparison priority.

Follow-up to #8491, which closed #8489.

Performance

Release on Windows, medians of three calibrated samples:

Operation (operand sizes)	Before	After
Native issubset (32/512)	27.632 µs	1.096 µs
Native isdisjoint (32/512)	20.375 µs	0.534 µs
Native intersection, larger left operand (512/32)	7.640 µs	2.350 µs
Set equality, custom-hash keys (32/32)	6.371 µs	0.465 µs
Intersection with a disjoint dict (8/128)	1.911 µs	3.790 µs

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Written with Codex (GPT-6), reviewed by a human before submission.

Summary by CodeRabbit

Bug Fixes
- Set and frozenset intersections, including in-place intersections, now handle multiple operands and set-like inputs more consistently.
- Subset, superset, and disjoint checks now behave more reliably with sets, frozensets, and custom iterables.
- Dictionary lookups and assignments now follow the expected key comparison order, including when equal keys have different identities.

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coderabbitai · 2026-09-27T08:38:00Z

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📝 Walkthrough

Walkthrough

Dictionary key comparisons now try the stored key before the lookup key. Set and frozenset intersection and relation operations use revised paths for set operands and generic iterables. Tests cover comparison order, hash calls, key identity, and iterator behavior.

Changes

Set and key comparison operations

Layer / File(s)	Summary
Dictionary key comparison order `crates/vm/src/dict_inner.rs`, `extra_tests/snippets/builtin_dict.py`	Fallback rich comparisons now pass the stored entry key before the lookup key. Tests cover lookup, assignment, deletion, and retention of the original key.
Set intersection and relation operations `crates/vm/src/builtins/set.rs`, `extra_tests/snippets/builtin_set.py`	Intersection and relation methods use stored hashes for set and frozenset operands. Generic intersection inputs are hashed once per item, and processing can stop when the result reaches the receiver’s size. Tests cover equality direction, key identity, mutation, and iterator errors.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Bug fix

Suggested reviewers: youknowone

Merge Risk: 🔵 Low · up to d6f49

A list containing an asymmetrically equal key can produce the wrong subset result. This is a narrow compatibility issue to fix before merging if feasible.

Security Architecture Review

Security architecture risk: 🟡 Moderate · up to d6f49

Set operations have broad use, and the new shortcut can make a subset check return true when a required member is absent if keys have unusual but permitted equality behavior. No application-level security bypass has been established.

Retained concerns

Medium · security · inferred: Generic intersection assumes that each distinct result key accounts for a distinct receiver member. With directional or non-transitive Python equality, that assumption can fail, causing an incomplete intersection and a false-positive issubset result.

Security review details

Security Blast Radius

inferred — The demonstrated exposure is to callers of VM set and frozenset operations with custom keys or generic iterables. No tenant, credential, network, or deployment authority change is evidenced.

Security Findings and Attack Paths

inferred — If two distinct supplied keys both compare equal to one stored receiver key but not to each other, they can fill the result to the receiver’s size before another receiver member is matched. This can make issubset return true; whether any host application uses that result for authorization is unknown.

Trust Boundaries and Controls

observed — Known-hash lookup still checks identity and hash before invoking key equality on a collision; the optimization does not omit equality evaluation. Generic operands still enter through iteration and hashing.

Resilience and Maintainability Implications

inferred — Staging limits mutation of the receiver when operand evaluation fails, but it does not make the new cardinality-based completion test valid under arbitrary equality or reentrant callbacks.

Hardening Proposals

proposed — Make generic-iterable early exit depend on proven coverage of distinct receiver members rather than result cardinality alone, and exercise directional-equality and reentrant-mutation cases.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 14.71% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 34 functions across 4 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the two main changes: reusing stored hashes in set operations and correcting key comparison order.
Linked Issues check	✅ Passed	Directly linked issue `#8489` is closed and supplies historical context only. No active directly linked issue remains, so this pull request has no linked-issue coding requirements.
Out of Scope Changes check	✅ Passed	The changed set and dictionary comparison code, plus the added set and dictionary tests, match the stated objectives for stored-hash reuse, set operations, and comparison order. The changes have a dir…

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Inline comments:
In @crates/vm/src/builtins/set.rs:
- Around line 407-416: Update the generic iterable fallback in issubset to
materialize other as a set and compare with PyComparisonOp::Le, rather than
using intersection; preserve the existing fast path for set operands.

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ℹ️ Review info

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Run ID: 35b0b58d-6f4a-40bb-99f9-0d672646459b

📥 Commits

Reviewing files that changed from the base of the PR and between 90afe00 and d6f4938.

📒 Files selected for processing (4)

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

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 8 remain after this review.

codspeed · 2026-09-27T08:56:48Z

Merging this PR will not alter performance

✅ 62 untouched benchmarks
⏩ 4 skipped benchmarks¹

_{Comparing 1ndahous3:set_native_ops (d6f4938) with main (90afe00)}

4 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

youknowone

👍

Reuse set hashes and fix stored key comparison order

d6f4938

Assisted-by: Codex:GPT-6

coderabbitai Bot reviewed Sep 27, 2026

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Comment thread crates/vm/src/builtins/set.rs

youknowone approved these changes Sep 27, 2026

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youknowone merged commit 360803f into RustPython:main Sep 27, 2026
22 checks passed

1ndahous3 deleted the set_native_ops branch September 27, 2026 13:54

1ndahous3 mentioned this pull request Sep 27, 2026

Avoid redundant work in set difference operations #8869

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Reuse stored hashes in set operations and fix key comparison order - #8852

Reuse stored hashes in set operations and fix key comparison order#8852
youknowone merged 1 commit into
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1ndahous3:set_native_ops

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1ndahous3 commented Sep 27, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

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codspeed Bot commented Sep 27, 2026

Merging this PR will not alter performance

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1ndahous3 commented Sep 27, 2026 •

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