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Return distinct empty lists from select() - #8720

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youknowone merged 1 commit into
RustPython:mainfrom
YangSiJun528:fix-select-list-identity
Sep 15, 2026
Merged

Return distinct empty lists from select()#8720
youknowone merged 1 commit into
RustPython:mainfrom
YangSiJun528:fix-select-list-identity

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@YangSiJun528

@YangSiJun528 YangSiJun528 commented Sep 15, 2026 •
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Summary

Return three distinct empty lists from select.select() instead of sharing one list, matching CPython. Remove expectedFailure from the existing regression test.

Validated with test_select, workspace and C-API tests, and Clippy.

AI assistance: Codex (gpt-6-astra) implemented the fix and ran validation.

Summary by CodeRabbit

  • Bug Fixes
    • Improved handling of empty input lists in the selection functionality, ensuring each returned result is an independent empty list.

@YangSiJun528
Return distinct empty lists from select()
cb8f7e5 
Assisted-by: Codex:gpt-6-astra
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coderabbitai Bot commented Sep 15, 2026 •
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Review Change StackReview Change Stack

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info
⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Advanced

Run ID: 282e95ee-bda3-4987-ba94-6708ca02abbf

📥 Commits

Reviewing files that changed from the base of the PR and between 8be1439 and cb8f7e5.

⛔ Files ignored due to path filters (1)
  • Lib/test/test_select.py is excluded by !Lib/**
📒 Files selected for processing (1)
  • crates/stdlib/src/select.rs

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

📝 Walkthrough

Walkthrough

The empty-input path in select now creates three independent empty PyList objects instead of cloning one list.

Changes

Select empty-result handling

Layer / File(s) Summary
Empty result construction
crates/stdlib/src/select.rs		 When all three input lists are empty, select creates a separate empty list for each returned value.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Bug fix

Suggested reviewers: youknowone

Merge Risk: ⚪ Minimal · up to cb8f7

The change aligns empty select results with the intended behavior and presents no identified merge-blocking risk.

🚥 Pre-merge checks | ✅ 5
✅ Passed checks (5 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly and concisely describes the main change: returning distinct empty lists from select().
Docstring Coverage ✅ Passed Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files.
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 github-actions Bot added the z-ca-2026 Tag to track Contribution Academy 2026 label Sep 15, 2026
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github-actions Bot commented Sep 15, 2026

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📦 Library Dependencies

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

[x] test: cpython/Lib/test/test_select.py (TODO: 2)
[x] test: cpython/Lib/test/test_poll.py (TODO: 1)

dependencies:

dependent tests: (109 tests)

  • select: test_asyncio test_devpoll test_epoll test_exception_hierarchy test_file_eintr test_imaplib test_kqueue test_os test_poll test_pty test_pyrepl test_repl test_select test_smtplib test_socket test_socketserver test_ssl test_subprocess
    • http.server: test_httpservers test_logging test_robotparser test_urllib2_localnet test_xmlrpc
      • pydoc: test_enum test_pydoc
      • wsgiref.simple_server: test_wsgiref
      • xmlrpc.server: test_docxmlrpc
    • pty: test_builtin
    • pydoc:
      • pdb: test_pdb
    • selectors: test_asyncio test_selectors
      • asyncio.selector_events: test_asyncio
      • socket: test_asyncio test_external_inspection test_ftplib test_httplib test_largefile test_mailbox test_mmap test_pathlib test_poplib test_signal test_smtpnet test_stat test_support test_sys test_timeout test_urllib test_urllib2 test_urllib2net test_urllib_response test_urllibnet
      • subprocess: test_android test_asyncio test_atexit test_audit test_bz2 test_c_locale_coercion test_cmd_line test_cmd_line_script test_ctypes test_dtrace test_embed test_faulthandler test_gc test_gzip test_inspect test_json test_launcher test_msvcrt test_ntpath test_osx_env test_peg_generator test_platform test_plistlib test_py_compile test_pyrepl test_quopri test_regrtest test_runpy test_script_helper test_shutil test_site test_sqlite3 test_sys_settrace test_sysconfig test_tempfile test_threading test_traceback test_unittest test_utf8_mode test_venv test_wait3 test_webbrowser test_xpickle test_zipfile
    • subprocess:
      • ctypes.util: test_ctypes
      • ensurepip: test_ensurepip
      • platform: test__locale test__osx_support test_baseexception test_cmath test_fcntl test_math test_mimetypes test_posix test_strptime test_time test_winreg

Legend:

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

ShaharNaveh
ShaharNaveh approved these changes Sep 15, 2026
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@ShaharNaveh ShaharNaveh left a comment

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sweet!

tysm:)

@youknowone
youknowone merged commit 3bdd2f9 into RustPython:main Sep 15, 2026
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@youknowone youknowone mentioned this pull request Sep 15, 2026
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youknowone pushed a commit that referenced this pull request Sep 16, 2026
@YangSiJun528 @youknowone
Return distinct empty lists from select() (#8720)
6cc0684 
Assisted-by: Codex:gpt-6-astra

(cherry picked from commit 3bdd2f9)
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@ShaharNaveh ShaharNaveh ShaharNaveh approved these changes

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@YangSiJun528 @ShaharNaveh @youknowone