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Match CPython's "argument of type ... is not a container or iterable" wording#7714

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youknowone merged 1 commit intoRustPython:mainfrom
changjoon-park:fix-contains-error-message
Apr 29, 2026
Merged

Match CPython's "argument of type ... is not a container or iterable" wording#7714
youknowone merged 1 commit intoRustPython:mainfrom
changjoon-park:fix-contains-error-message

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@changjoon-park changjoon-park commented Apr 28, 2026 •
edited by coderabbitai Bot
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Background

CPython's PySequence_Contains (Objects/abstract.c::_PySequence_IterSearch) catches the TypeError from PyObject_GetIter when neither __contains__ nor __iter__ is available, and re-raises with membership-test wording:

TypeError: argument of type 'X' is not a container or iterable

RustPython's PySequence::contains propagated the get_iter error verbatim, so 1 in obj produced 'X' object is not iterable — a literal but less specific message.

Repro

class X: pass
1 in X()
# CPython 3.14:    TypeError: argument of type 'X' is not a container or iterable
# RustPython:      TypeError: 'X' object is not iterable    (before this PR)

Fix

Wrap the get_iter(vm) call inside PySequence::contains in map_err. When the failure is a TypeError (the "not iterable" case), re-raise with the byte-identical CPython membership-test wording. Other exception types (e.g. propagated from a user __iter__) pass through unchanged.

Tests unmasked

  • test_contains.TestContains.test_common_tests

Verification

  • CPython 3.14.4 byte-identical for the bare-class case
  • Types with __contains__ (str/tuple/dict/set/list/...): unchanged — they go through the slots().contains path before reaching this site
  • Types with only __iter__: unchanged — get_iter succeeds
  • No regressions across 8 modules (~1,349 tests): test_contains, test_iter, test_dict, test_set, test_list, test_tuple, test_str, test_bytes

Summary by CodeRabbit

Bug Fixes

  • Improved error messages for membership testing: TypeError messages when testing membership on non-container or non-iterable objects now align with CPython's standard wording for better consistency.

@changjoon-park
Match CPython's "argument of type ... is not a container or iterable"…
aab298f 
… wording

CPython's PySequence_Contains (Objects/abstract.c::_PySequence_IterSearch)
catches the TypeError from PyObject_GetIter when neither __contains__ nor
__iter__ is available, and re-raises with membership-test wording.

RustPython's PySequence::contains propagated the get_iter error verbatim,
so '1 in obj' produced 'X' object is not iterable — a literal but less
specific message.

Wrap the get_iter call in map_err: when the failure is a TypeError,
re-raise with byte-identical CPython wording. Other exception types pass
through unchanged.

Unmasks test_contains.TestContains.test_common_tests.
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coderabbitai Bot commented Apr 28, 2026 •
edited
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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: 769ad4e3-40bb-4141-91f7-262854b6d9f6

📥 Commits

Reviewing files that changed from the base of the PR and between 3f718f9 and aab298f.

⛔ Files ignored due to path filters (1)
  • Lib/test/test_contains.py is excluded by !Lib/**
📒 Files selected for processing (1)
  • crates/vm/src/protocol/sequence.rs
📝 Walkthrough

Walkthrough

PySequence::contains method now intercepts TypeError exceptions from get_iter(vm) and rewrites them to match CPython's membership-test error message. Other exception types are propagated unchanged. The module imports AsObject from the crate.

Changes

Cohort / File(s) Summary
Error Message Standardization
crates/vm/src/protocol/sequence.rs		 Updated PySequence::contains to intercept and rewrite TypeError from get_iter(vm) to match CPython's membership-test error wording ("not a container or iterable"). Added AsObject import from crate.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Suggested reviewers

  • youknowone
  • ShaharNaveh

Poem

🐰 A tiny fix, so clean and bright,
Where error messages now align just right—
CPython's words now echo here,
In containers and iterables, crystal clear! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ 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%. 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 directly describes the main change: matching CPython's error message wording for membership tests. It accurately reflects the primary objective of the PR.
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 Apr 28, 2026

📦 Library Dependencies

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

[x] test: cpython/Lib/test/test_contains.py

dependencies:

dependent tests: (no tests depend on contains)

Legend:

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

ShaharNaveh
ShaharNaveh approved these changes Apr 28, 2026
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great! tysm:)

@changjoon-park
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changjoon-park commented Apr 28, 2026

great! tysm:)

thanks for the review !

@youknowone youknowone merged commit 04ffa38 into RustPython:main Apr 29, 2026
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@youknowone youknowone youknowone approved these changes

@ShaharNaveh ShaharNaveh ShaharNaveh approved these changes

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3 participants

@changjoon-park @youknowone @ShaharNaveh