Python ignores whitespace in format strings#6447

youknowone

Summary by CodeRabbit

Chores
- Updated spell-check dictionary with new entries.
Bug Fixes
- Improved format string parsing to gracefully handle whitespace characters after repeat counts, providing clearer error messaging when format specifiers are missing or malformed.

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coderabbitai

Walkthrough

This PR adds three new spell-check dictionary entries (DICTFLAG, keeped, stginfo) and modifies the struct format string parser in the buffer module to skip whitespace after repeat counts and handle missing format specifiers based on whether a non-default repeat was specified.

Changes

Cohort / File(s)	Summary
Spell-check dictionary `.cspell.dict/cpython.txt`	Added three new entries: `DICTFLAG`, `keeped`, and `stginfo` to the allowed words list.
Struct format parsing `crates/vm/src/buffer.rs`	Modified format string parser to skip whitespace (space, tab, newline, carriage return) after repeat counts. Adjusted logic to read the format character after whitespace, with conditional error handling: returns error if no format character follows a non-default repeat count (repeat != 1), otherwise stops parsing gracefully.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

buffer.rs logic: Requires verification that whitespace-skipping doesn't inadvertently consume format specifiers and that error conditions (missing specifier vs. default repeat) are correctly handled.
Dictionary entries: Confirm these are intentional keyword additions without typos.

Poem

🐰 A hopping through format strings with glee,
Whitespace begone! We skip merrily,
Three words join the spell-check spree,
Parsing cleaner, errors run free! ✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding whitespace handling in format string parsing, which aligns with the buffer.rs modifications.

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

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Actionable comments posted: 1

📜 Review details

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 272b36d and 61a032d.

📒 Files selected for processing (2)

.cspell.dict/cpython.txt (3 hunks)
crates/vm/src/buffer.rs (1 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

**/*.rs

📄 CodeRabbit inference engine (.github/copilot-instructions.md)

**/*.rs: Follow the default rustfmt code style by running cargo fmt to format Rust code
Always run clippy to lint Rust code (cargo clippy) before completing tasks and fix any warnings or lints introduced by changes
Follow Rust best practices for error handling and memory management
Use the macro system (pyclass, pymodule, pyfunction, etc.) when implementing Python functionality in Rust

Files:

crates/vm/src/buffer.rs

🔇 Additional comments (2)

crates/vm/src/buffer.rs (2)

241-244: No changes required—Python whitespace handling is correctly implemented.

The code at lines 241-244 correctly skips the standard ASCII whitespace characters (space, tab, newline, carriage return) that Python's struct module ignores in format strings. The comment and implementation are both accurate.

247-257: Logic is correct; add edge case tests for whitespace handling.

The implementation correctly handles format parsing with whitespace based on the official Python struct documentation. The error logic for "repeat count given without format specifier" appropriately distinguishes between explicit repeat counts and default repeats when trailing whitespace is encountered.

Consider adding tests to extra_tests/snippets/stdlib_struct.py to explicitly verify edge cases:

Format with trailing whitespace: "i "

Explicit repeat with trailing whitespace: "3i "

Whitespace between repeat and format: "3 i"

These scenarios are not currently covered in the test file.

fix buffer

61a032d

youknowone marked this pull request as ready for review December 16, 2025 14:10

coderabbitai Bot reviewed Dec 16, 2025

View reviewed changes

youknowone deleted the buffer branch December 16, 2025 14:27

coderabbitai Bot mentioned this pull request Feb 17, 2026

Update ctypes from v3.14.3 and make _ctypes compatible #7165

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Python ignores whitespace in format strings#6447