GeezerVison is showing github.com — Keep a bytearray exported while it formats with % by luantaraschi · Pull Request #9147 · RustPython/RustPython
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luantaraschi
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Oct 15, 2026
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edited by coderabbitai
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Summary
test_mod_concurrent_mutation in test_bytes was still skipped as a segfault. #8524 fixed the crash by formatting a copy of the bytearray, but nothing stopped a conversion callback from resizing the format meanwhile, so the test's BufferError never came:
fmt = bytearray(b"%a end")
class S:
def __repr__(self):
fmt.clear()
return "E"
fmt % S()
Here this returned bytearray(b'E end') and left fmt empty. CPython 3.15 raises BufferError: Existing exports of data: object cannot be re-sized and fmt keeps b"%a end".
__mod__ now holds an export for the whole call, which is what join already does for its separator. The format is still copied, so one thing still differs: an in-place change that keeps the length (e.g. fmt[4] = ord("r") from inside __bytes__) is not seen, where CPython formats the changed buffer. No CPython test covers that, and fixing it means not copying, so I left it.
With the skip removed, the test fails before the change (BufferError not raised by __mod__) and passes after. Nine variants of this case match CPython 3.15.0. test_bytes passes 3 runs out of 3, and test_memoryview, test_buffer and test_format pass too. Workspace cargo test with the AGENTS.md excludes, clippy -Dwarnings, cargo fmt --check and the prek hooks (including check_redundant_patches) are clean. Linux release build only.
Written with Claude Code (claude-opus-5-5) as a tool, and I went over the change and the results before opening this.
Summary by CodeRabbit
- Bug Fixes
- Bytearray formatting now prevents the bytearray from being resized while value-conversion callbacks are running.
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bytearray.__mod__ copied the format and ran the arguments' __repr__,
__str__, __bytes__ and __index__ without holding an export, so a callback
could clear or extend the format and formatting went on with the old
copy:
fmt = bytearray(b"%a end")
class S:
def __repr__(self):
fmt.clear()
return "E"
fmt % S() # bytearray(b'E end'), fmt left empty
CPython holds a buffer on the format for the whole call, so the resize
fails with BufferError and the format is left as it was. Taking an export
for the duration of __mod__ does the same here, the way bytearray.join
already does for its separator.
This lets test_mod_concurrent_mutation in test_bytes run again.
Assisted-by: Claude Code:claude-opus-5-5
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⚠️ Failed 2026-10-15T10:21:27.792231Z |
2feef00 |
PR opened |
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coderabbitai
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Oct 15, 2026
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edited
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No actionable comments were generated in the recent review. 🎉
ℹ️ Recent review info
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⚙️ Run configuration
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- Configuration used: Repository: RustPython/RustPython/.coderabbit.yml
- Review profile: CHILL
- Plan: Advanced
- Run ID:
e1cb7734-cd23-4ff7-9328-a0cec533212e
📥 Commits
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Reviewing files that changed from the base of the PR and between 16e333b and 2feef00.
⛔ Files ignored due to path filters: 1
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Lib/test/test_bytes.py is excluded by !Lib/**
📒 Files selected for processing: 1
-
crates/vm/src/builtins/bytearray.rs
Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 9 remain after this review.
📝 Walkthrough
-
PyByteArray.__mod__ now holds a buffer export while it clones the format and runs formatting. This keeps the bytearray exported while value-conversion callbacks run.
Changes: Bytearray formatting
| Layer / File(s) |
Summary |
Hold export during formatting crates/vm/src/builtins/bytearray.rs |
__mod__ begins a buffer export before cloning the format and invoking formatting. This keeps the export active during conversion callbacks. |
Priority: ⬇️ Low
Estimated code review effort: 2 (Simple) | ~5 minutes
Change: Bug fix
Suggested reviewers: youknowone
Merge Risk: ⚪ Minimal · up to 2feef
-
Formatting now rejects callback-triggered resizing with BufferError; no merge-blocking issue is established.
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 1 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 and concisely describes the main change: keeping the bytearray exported during % formatting. |
| Linked Issues check |
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Check skipped because no linked issues were found for this pull request. |
| Out of Scope Changes check |
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Check skipped because no linked issues were found for this pull request. |
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📦 Library Dependencies
The following Lib/ modules were modified. Here are their dependencies:
:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
:4: SyntaxWarning: invalid decimal literal
:7: SyntaxWarning: "\z" is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\z"? A raw string is also an option.
:10: SyntaxWarning: "\400" is an invalid octal escape sequence. Such sequences will not work in the future. Did you mean "\400"? A raw string is also an option.
[ ] lib: cpython/Lib/concurrent
[ ] test: cpython/Lib/test/test_concurrent_futures (TODO: 1)
[ ] test: cpython/Lib/test/test_interpreters
[ ] test: cpython/Lib/test/test__interpreters.py
[ ] test: cpython/Lib/test/test__interpchannels.py
[ ] test: cpython/Lib/test/test_crossinterp.py
dependencies:
- concurrent (native: _crossinterp, _interpqueues, _interpreters, _queues, concurrent.futures, concurrent.futures._base, interpreter, itertools, multiprocessing.connection, multiprocessing.queues, multiprocessing.synchronize, process, sys, thread, time)
- collections (native: _collections, _weakref, itertools, sys)
- functools (native: _functools, _thread)
- multiprocessing (native: _multiprocessing, _posixshmem, _posixsubprocess, _winapi, array, atexit, collections.abc, connection, context, dummy, errno, forkserver, heap, itertools, managers, mmap, msvcrt, multiprocessing.connection, pool, popen_fork, popen_forkserver, popen_spawn_posix, popen_spawn_win32, queues, resource_sharer, resource_tracker, sharedctypes, spawn, synchronize, sys, time, util, xmlrpc.client)
- os (native: nt, os.path, posix, sys)
- threading (native: _collections, _contextvars, _thread, itertools, sys, time)
- traceback (native: _missing_stdlib_info, _suggestions, collections.abc, importlib.machinery, importlib.resources.readers, importlib.util, itertools, sys, unicodedata)
- types (native: _types, sys)
- weakref (native: _weakref, atexit, gc, itertools, sys)
- logging, queue
dependent tests: (17 tests)
- concurrent: test_asyncio test_compileall test_concurrent_futures test_context test_genericalias test_inspect test_struct test_sys test_threading test_types test_wmi
- asyncio: test_asyncio test_external_inspection test_logging test_os test_pdb test_unittest
[ ] lib: cpython/Lib/asyncio
[ ] test: cpython/Lib/test/test_asyncio (TODO: 3)
dependencies:
- asyncio (native: _asyncio, _overlapped, _pyrepl.console, _pyrepl.main, _pyrepl.simple_interact, _remote_debugging, _winapi, asyncio.tools, base_events, collections.abc, concurrent.futures, coroutines, errno, events, exceptions, futures, graph, itertools, locks, log, math, msvcrt, protocols, queues, readline, runners, streams, sys, taskgroups, tasks, threads, time, timeouts, transports, unix_events, windows_events)
- _colorize (native: builtins, collections.abc, nt, sys)
- argparse (native: sys)
- ast (native: _ast, sys)
- code (native: builtins, readline, sys)
- contextlib (native: sys)
- dataclasses (native: itertools, sys)
- inspect (native: _weakref, builtins, collections.abc, importlib.machinery, itertools, sys)
- io (native: _io, _thread, errno, msvcrt, sys)
- linecache (native: sys)
- rlcompleter (native: main, atexit, builtins, readline)
- site (native: _io, _pyrepl.main, _pyrepl.pager, _pyrepl.readline, _pyrepl.unix_console, _pyrepl.windows_console, atexit, builtins, errno, readline, sitecustomize, sys, usercustomize)
- socket (native: _socket, array, errno, sys)
- ssl (native: _ssl, errno, sys, time)
- stat (native: _stat)
- subprocess (native: _posixsubprocess, _winapi, builtins, errno, fcntl, grp, msvcrt, pwd, select, sys, time)
- tokenize (native: _tokenize, builtins, itertools, sys)
- collections, functools, os, threading, traceback, types, weakref
- contextvars, enum, heapq, logging, reprlib, selectors, signal, struct, warnings
dependent tests: (8 tests)
- asyncio: test_asyncio test_concurrent_futures test_external_inspection test_inspect test_logging test_os test_pdb test_unittest
[ ] test: cpython/Lib/test/test_bytes.py (TODO: 14)
dependencies:
dependent tests: (no tests depend on bytes)
Legend:
[+] path exists in CPython
[x] up-to-date, [ ] outdated
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