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GeezerVison is showing github.com — Fix swapcase() by joshuamegnauth54 · Pull Request #7788 · RustPython/RustPython

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joshuamegnauth54 commented May 5, 2026 •

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The tests for swapcase() were failing for two reasons. The first is '𐐧' casing which should be fixed with modern Unicode tables. The second failure is due to CPython's sigma override, which I implemented in #7117.

~~This should work after rebasing, so I'm opening it as a placeholder for now. 😸~~ Ready since #7117 is merged.

Summary by CodeRabbit

Refactor
- Optimized text case operations: faster ASCII fast paths and a new UTF‑8 swapcase routine for improved performance.
- Byte-level case swapping now uses a streamlined ASCII path; invalid or non-UTF‑8 bytes are preserved during UTF‑8 processing.

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coderabbitai Bot commented May 5, 2026 •

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 3fb1ce6e-d430-41e3-9be8-308086cd8a47

📥 Commits

Reviewing files that changed from the base of the PR and between e4ba68f and b7ad7c4.

⛔ Files ignored due to path filters (1)

Lib/test/test_str.py is excluded by !Lib/**

📒 Files selected for processing (2)

crates/vm/src/builtins/str.rs
crates/vm/src/bytes_inner.rs

🚧 Files skipped from review as they are similar to previous changes (2)

crates/vm/src/builtins/str.rs
crates/vm/src/bytes_inner.rs

📝 Walkthrough

Walkthrough

Adds a crate-local ASCII swapcase helper, makes bytes swapcase delegate to it, imports helpers into str.rs, and refactors PyStr::swapcase to dispatch by encoding kind with a new UTF‑8-aware swapcase routine.

Changes

Swapcase refactoring with per-kind helpers

Layer / File(s)	Summary
Shared ASCII swapcase helper and bytes integration `crates/vm/src/bytes_inner.rs`	`pub(crate) fn swapcase_ascii(bytes: &[u8]) -> Vec<u8>` flips ASCII letters via XOR `0x20`. `PyBytesInner::swapcase` now delegates to this helper.
str imports and title ASCII call `crates/vm/src/builtins/str.rs`	Import list updated to bring `swapcase_ascii` and `title_ascii` into scope. `PyStr::title()` ASCII branch now calls `title_ascii`.
PyStr swapcase dispatch and UTF-8 implementation `crates/vm/src/builtins/str.rs`	`PyStr::swapcase()` now dispatches on `StrKind`: ASCII -> `swapcase_ascii`, UTF-8 -> `swapcase_utf8`, WTF-8 -> apply `swapcase_utf8` to valid chunks and preserve invalid/surrogate bytes. Adds `swapcase_utf8` that iterates `char_indices()` and uses `lowercase_or_sigma` / `to_uppercase` with correct multi-char expansion.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

RustPython/RustPython#7748: Overlaps with changes to PyStr::title() and ASCII title handling.
RustPython/RustPython#7559: Related Unicode-aware PyStr::swapcase improvements with multibyte expansion.
RustPython/RustPython#7717: Related edits to PyStr::title() and titlecasing logic.

Suggested reviewers

ShaharNaveh
youknowone

Poem

🐰 I hop through bytes and strings tonight,
XOR flips ASCII with nimble might,
UTF‑8 letters bloom and spread,
Surrogate bytes stay safe, unfed,
Swapcase done — a rabbit’s delight!

🚥 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%.	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 'Fix swapcase()' directly refers to the main change: refactoring and fixing the swapcase() method implementation across multiple files to use optimized helpers and handle Unicode properly.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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github-actions Bot commented May 5, 2026 •

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📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] test: cpython/Lib/test/test_str.py (TODO: 7)
[x] test: cpython/Lib/test/test_fstring.py (TODO: 19)
[x] test: cpython/Lib/test/test_string_literals.py (TODO: 4)

dependencies:

dependent tests: (no tests depend on str)

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

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joshuamegnauth54 marked this pull request as ready for review

May 13, 2026 02:21

joshuamegnauth54 force-pushed the swapcase-fixes branch from 36c57da to e4ba68f Compare

May 13, 2026 02:21

coderabbitai Bot reviewed

May 13, 2026

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Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/vm/src/builtins/str.rs`:
- Around line 1664-1676: In swapcase_utf8, don’t treat every non-uppercase char
as lowercase; instead preserve titlecase and other uncased characters. Change
the branching so that if ch.is_uppercase() you call lowercase_or_sigma(ch, s, i,
out); else if ch.is_lowercase() you perform the to_uppercase() path and write
the uppercase bytes to out. For the remaining case (neither is_uppercase nor
is_lowercase, e.g. titlecase, digits, punctuation) copy the original char’s
UTF‑8 bytes into out unchanged. This touches swapcase_utf8 and reuses
lowercase_or_sigma for the uppercase->lowercase work.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

Push a commit to this branch (recommended)
Create a new PR with the fixes

ℹ️ Review info

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Run ID: 06ccac61-207a-4696-bbb2-271a962b34f6

📥 Commits

Reviewing files that changed from the base of the PR and between 5ef91c2 and e4ba68f.

⛔ Files ignored due to path filters (1)

Lib/test/test_str.py is excluded by !Lib/**

📒 Files selected for processing (2)

crates/vm/src/builtins/str.rs
crates/vm/src/bytes_inner.rs

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Comment thread

crates/vm/src/builtins/str.rs Resolved

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          Fix swapcase()

b7ad7c4

The tests for swapcase() were failing for two reasons. The first is
'𐐧' casing which should be fixed with modern Unicode tables. The second
failure is due to CPython's sigma override, which I implemented in
PR RustPython#7717.

joshuamegnauth54 force-pushed the swapcase-fixes branch from e4ba68f to b7ad7c4 Compare

May 13, 2026 02:48

youknowone approved these changes

May 13, 2026

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youknowone merged commit ef375be into RustPython:main

May 13, 2026

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joshuamegnauth54 deleted the swapcase-fixes branch

May 16, 2026 17:35

youknowone pushed a commit that referenced this pull request

Sep 16, 2026


          Fix swapcase() (#7788)

e59f2a7

The tests for swapcase() were failing for two reasons. The first is
'𐐧' casing which should be fixed with modern Unicode tables. The second
failure is due to CPython's sigma override, which I implemented in
PR #7717.

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coderabbitai[bot]

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joshuamegnauth54 commented May 5, 2026 • edited by coderabbitai Bot Loading Uh oh! There was an error while loading. Please reload this page.

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Summary by CodeRabbit

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Walkthrough

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📦 Library Dependencies

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joshuamegnauth54 commented May 5, 2026 •

edited by coderabbitai Bot

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