Fix set in-place operators with self argument by HueCodes · Pull Request #6661 · RustPython/RustPython

HueCodes · 2026-01-06T02:13:52Z

Fixes #3881
close #3912
close #4424
close #4708

When a set performs in-place operations with itself (s &= s, s -= s, s ^= s), the operators now handle the self-reference case correctly:

__iand__: no-op (intersection with self is unchanged)
__isub__: clear (difference with self is empty)
__ixor__: clear (symmetric difference with self is empty)

Summary by CodeRabbit

Bug Fixes
- Corrected behavior of in-place set operations (&=, -=, ^=) when a set operates on itself, preventing unintended modifications.
Tests
- Added test cases validating in-place set operations when operating on the same set instance.

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coderabbitai · 2026-01-06T02:14:04Z

📝 Walkthrough

Walkthrough

The changes add self-reference checks to in-place set operations (__iand__, __isub__, __ixor__) in the VM builtins to prevent redundant operations when a set operates on itself. A helper method detects self-references, and corresponding test cases validate the corrected behavior.

Changes

Cohort / File(s)	Change Summary
Set In-Place Operations Self-Reference Handling `crates/vm/src/builtins/set.rs`	Added `is_same_object(&self, other: &PyObject) -> bool` helper method to detect self-references. Modified `__iand__`, `__isub__`, and `__ixor__` to short-circuit when the operand is the same object: intersection with self remains unchanged, difference and XOR with self clear the set.
Test Cases for Set In-Place Self Operations `extra_tests/snippets/builtin_set.py`	Added test cases for in-place set operations on self: `a &= a` (unchanged), `a -= a` (clears), `a ^= a` (clears), with assertions verifying expected results.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

Avoid set changed size during iteration #5860: Both PRs address in-place set operations when the operand is the same object, with complementary fixes to iteration and self-checking logic.

Suggested reviewers

arihant2math

Poem

🐰 Whiskers twitch with glee,
Sets now know when self they see—
a &= a stays true,
a -= a makes it new (empty!),
Pythonic magic, tried and true! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 60.00% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing set in-place operators when used with self argument, matching the primary objective.
Linked Issues check	✅ Passed	The PR successfully implements all three required fixes from issue #3881: iand handles self-reference correctly (no-op), isub clears the set, and ixor clears the set, matching CPython behavior.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the linked issue requirements: conditionals in in-place set operators and test cases validate the self-reference behavior.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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ShaharNaveh

lgtm

fanninpm · 2026-01-06T16:56:14Z

Could you please rebase this branch on a fresh copy of main?

HueCodes · 2026-01-06T19:58:10Z

Yes! I will rebase this afternoon when I get home. Thanks for the quick response.

youknowone

Thank you for contributing! The operation parts are looking perfect!
I left a suggestion to replace is_same_object to common RustPython internal mechanism. Please check it.

youknowone · 2026-01-08T11:04:35Z

crates/vm/src/builtins/set.rs

+    fn is_same_object(&self, other: &PyObject) -> bool {
+        self.object.is(other)
+    }


We have a mechanism to do this.

is is not a method of PyObject, but an object ofAsObject. And PyObject is implementing AsObject through Borrow.

AnySet can do the same thing.
impl Borrow<PyObject> for AnySet {}
will enable AsObject for AnySet. Then set.is_same_object(zelf.as_object()) above can be simply written as set.is(zelf.as_object())

HueCodes · 2026-01-09T05:24:35Z

Done.

youknowone

Great! Thank you so much for contributing!

Co-authored-by: Hugh <[email protected]>

ShaharNaveh approved these changes Jan 6, 2026

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HueCodes force-pushed the fix-set-inplace-self-ops branch from 7a72db2 to 36bace4 Compare January 7, 2026 00:02

youknowone requested changes Jan 8, 2026

View reviewed changes

Fix set in-place operators with self argument

dcbf4fb

HueCodes force-pushed the fix-set-inplace-self-ops branch from 36bace4 to dcbf4fb Compare January 9, 2026 05:23

youknowone approved these changes Jan 9, 2026

View reviewed changes

youknowone merged commit 83a0dea into RustPython:main Jan 9, 2026
13 checks passed

terryluan12 pushed a commit to terryluan12/RustPython that referenced this pull request Jan 15, 2026

Fix set in-place operators with self argument (RustPython#6661)

4f66dec

Co-authored-by: Hugh <[email protected]>

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Fix set in-place operators with self argument#6661

Fix set in-place operators with self argument#6661
youknowone merged 1 commit intoRustPython:mainfrom
HueCodes:fix-set-inplace-self-ops

HueCodes commented Jan 6, 2026 •

edited by youknowone

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HueCodes commented Jan 6, 2026 •

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