Make SystemExit.code a writable attribute set at init by kangdora · Pull Request #8282 · RustPython/RustPython

kangdora · 2026-07-14T00:13:41Z

Closes SystemExit.code is read-only; CPython allows assignment #8230
This PR follows our AI policy

Summary

SystemExit.code was a read-only getset recomputed from args on
every access, so assigning or deleting exc.code raised
AttributeError, and mutating exc.args after init changed code.
It is now stored in a dedicated struct field (#[repr(C)] with a
PyBaseException base, the same approach as OSError), set at
__init__ time — writable, deletable, and independent from args
after init, as in CPython. Keeping it in a field rather than the
instance dict leaves SystemExit().__dict__ empty, matching CPython.

A second commit updates handle_exit_exception to read the exit
status from the code attribute like CPython's handle_system_exit;
without it, reassigning exc.code would not affect the process exit
status:

import sys
try:
    sys.exit(1)
except SystemExit as e:
    e.code = 0   # before: AttributeError: ... not writable
    raise
# process exit status — before: 1, after: 0 (matches CPython)

Test plan

Verified against CPython 3.14.6: attribute write/delete including the subclass repro from SystemExit.code is read-only; CPython allows assignment #8230, exit statuses for sys.exit() /
sys.exit(3) / sys.exit('msg') / raise SystemExit(1, 2), and the re-raise case above.
Lib/test/test_exceptions.py, Lib/test/test_sys.py: no regressions (the single test_badisinstance failure is pre-existing on main).
test_threading / test_io thread-finalization cases pass (SystemExit is
now created via the full constructor path, not new_exception).
cargo fmt / cargo clippy: clean (no new warnings).

Assisted-by: Claude Code:claude-fable-5

Summary by CodeRabbit

Bug Fixes
- Improved handling of SystemExit during termination, including finalization and non-main threads.
- Exit codes are now derived from SystemExit.code (with None mapping to 0; integer values supported).
- SystemExit output is generated more reliably from the code value when present.
- SystemExit created via exit (and internal thread exit) now follows the same raising path, ensuring consistent behavior with provided exit values.

coderabbitai · 2026-07-14T00:14:22Z

📝 Walkthrough

Walkthrough

SystemExit now stores a writable code attribute initialized from positional arguments. Exit paths invoke SystemExit through the VM, and exit handling reads code to determine the numeric status or printable message.

Changes

SystemExit code lifecycle

Layer / File(s)	Summary
SystemExit code storage `crates/vm/src/exceptions.rs`	`SystemExit.code` is stored on the instance, supports assignment and deletion, is initialized from positional argument arity, and is included in traversal.
SystemExit raising paths `crates/vm/src/stdlib/_thread.rs`, `crates/vm/src/stdlib/builtins.rs`, `crates/vm/src/vm/mod.rs`	Exit functions and the finalization signal path invoke SystemExit through `VirtualMachine::invoke_exception`.
Exit exception extraction `crates/vm/src/vm/mod.rs`	Exit handling reads `code`, maps integers and `None` to exit statuses, and converts other values to messages with `str()`.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant ExitAPI
  participant VirtualMachine
  participant PySystemExit
  ExitAPI->>VirtualMachine: invoke SystemExit with exit arguments
  VirtualMachine->>PySystemExit: initialize writable code
  PySystemExit-->>VirtualMachine: raised SystemExit
  VirtualMachine->>PySystemExit: read code
  PySystemExit-->>VirtualMachine: integer, None, or other value
  VirtualMachine-->>ExitAPI: exit status or printable message

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes make SystemExit.code writable, store it independently after init, and use the reassigned value for exit status.
Out of Scope Changes check	✅ Passed	All edited paths directly support SystemExit.code semantics and exit handling, with no unrelated feature additions.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: SystemExit.code is now writable and initialized during exception setup.

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests

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coderabbitai

🧹 Nitpick comments (1)

crates/vm/src/exceptions.rs (1)
1658-1676: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Move the BaseException_init note to the PyBaseException::slot_init call below. The current placement describes the match above, not the call it refers to.
🤖 Prompt for 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.

In `@crates/vm/src/exceptions.rs` around lines 1658 - 1676, Move the “Call
BaseException_init first (handles args)” comment from above the code match in
PySystemExit::slot_init to immediately above the PyBaseException::slot_init
call, so it documents the call it refers to.
Source: Coding guidelines

🤖 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.

Nitpick comments:
In `@crates/vm/src/exceptions.rs`:
- Around line 1658-1676: Move the “Call BaseException_init first (handles args)”
comment from above the code match in PySystemExit::slot_init to immediately
above the PyBaseException::slot_init call, so it documents the call it refers
to.

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 6a9aa971-2421-42b9-9cad-54153f7ebee2

📥 Commits

Reviewing files that changed from the base of the PR and between 4d6ac3f and fb8f7b1.

📒 Files selected for processing (1)

crates/vm/src/exceptions.rs

youknowone

looks great, thanks! welcome to RustPython project!

note about the change: once we couldn't set getset to exception subtypes. that restriction was resolved early this year, but this one was not updated for a while.

kangdora added 3 commits July 13, 2026 22:28

Make SystemExit.code a writable attribute set at init

7ed3e04

Read exit status from SystemExit.code in handle_exit_exception

58652ba

Merge branch 'RustPython:main' into fix-systemexit-code

4d6ac3f

Store SystemExit.code in a struct field instead of the instance dict

fb8f7b1

coderabbitai Bot reviewed Jul 14, 2026

View reviewed changes

Create SystemExit through the full constructor path

9d3d2de

youknowone added the z-ca-2026 Tag to track Contribution Academy 2026 label Jul 15, 2026

youknowone approved these changes Jul 15, 2026

View reviewed changes

youknowone merged commit a1130dd into RustPython:main Jul 15, 2026
26 checks passed

This was referenced Jul 16, 2026

StopIteration.value is stored in the instance dict instead of as a member #8290

Closed

Store StopIteration.value in a struct field instead of the instance dict #8301

Merged

coderabbitai Bot mentioned this pull request Jul 20, 2026

Take a borrow in invoke_exception instead of an owned type #8327

Merged

2 tasks

kangdora mentioned this pull request Jul 21, 2026

Several built-in exceptions store their attributes in the instance dict instead of as fields #8345

Open

devyubin mentioned this pull request Jul 22, 2026

Store SyntaxError members in struct fields instead of the instance dict #8348

Open

1 task

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Make SystemExit.code a writable attribute set at init#8282

Make SystemExit.code a writable attribute set at init#8282
youknowone merged 5 commits into
RustPython:mainfrom
kangdora:fix-systemexit-code

kangdora commented Jul 14, 2026 •

edited

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coderabbitai Bot commented Jul 14, 2026 •

edited

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kangdora commented Jul 14, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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kangdora commented Jul 14, 2026 •

edited

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coderabbitai Bot commented Jul 14, 2026 •

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