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upgrade-pylib

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Upgrade a Python standard library module from CPython into RustPython using scripts/update_lib and then triage and mark remaining failures.

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Upgrade Python Library from CPython

Upgrade a Python standard library module from CPython to RustPython.

Arguments

  • Library name or path (examples: inspect, asyncio, json, cpython/Lib/inspect.py, cpython/Lib/json/)

Important: Report Tool Issues First

If scripts/update_lib shows a bug, missing automation, or unexpected behavior, stop the upgrade and report the tooling issue first, including:

  1. What you were trying to do:
  • Library name.
  • Full command used.
  1. What went wrong or what is missing.
  2. Expected vs actual behavior.

Workflow

  1. Run quick upgrade with update_lib:
  • python3 scripts/update_lib quick <module>
  • or python3 scripts/update_lib quick cpython/Lib/<module>.py
  • or python3 scripts/update_lib quick cpython/Lib/<module>/

This step copies library files, patches tests while preserving markers where possible, runs tests, auto-marks new failures, removes stale @unittest.expectedFailure, and creates a commit.

If warnings like WARNING: TestCFoo does not exist in remote file appear, class structure changed and some markers must be restored manually.

  1. Review diff and restore RustPython-specific changes:
  • Run git diff Lib/test/test_<module>.
  • Restore only changes with explicit RUSTPYTHON comments.
  • Do not restore unrelated upstream CPython changes.
  1. Investigate failing dependent tests:

  • Get dependencies:

    cargo run --release -- scripts/update_lib deps <module>

  • Find direct dependent test modules from the - [ ] <module>: line.

  • Run dependent tests and collect failures:

    cargo run --release -- -m test <test_modules...> 2>&1 | grep -E "^(FAIL|ERROR):"

  • For each failing test identifier, investigate with the investigate-test-failure workflow.

  1. Mark remaining failures with auto-mark:
  • python3 scripts/update_lib auto-mark Lib/test/test_<module>.py --mark-failure
  • or python3 scripts/update_lib auto-mark Lib/test/test_<module>/ --mark-failure

Note: --mark-failure marks all current failures including regressions; review carefully.

  1. Handle panics manually:
  • For tests that panic/crash/hang, use @unittest.skip("TODO: RUSTPYTHON; ...") rather than expectedFailure.
  1. Handle class-specific failures:
  • If only one subclass fails (for example TestCFoo but not TestPyFoo), move marker to the failing subclass override.
  1. Commit test-fix markers as a separate commit:
git add -u && git commit -m "Mark failing tests"

Example usage

upgrade-pylib inspect
upgrade-pylib json
upgrade-pylib asyncio
upgrade-pylib cpython/Lib/inspect.py
upgrade-pylib cpython/Lib/json/

Notes

  • The cpython/ directory should contain the CPython source used for sync.
  • scripts/update_lib modes:
    • quick: patch + auto-mark
    • migrate: patch only
    • auto-mark: mark failures only
    • copy-lib: copy library files only
  • Patching transfers @unittest.expectedFailure and @unittest.skip with TODO: RUSTPYTHON markers where possible.
  • The tool does not preserve every RustPython-specific change; always review and restore explicit RUSTPYTHON-marked logic.