# ruff G010: fix changes program behavior Internal evidence sheet generated by fixhunt. Not an issue text. A human re-verifies, checks the duplicates below, and writes the upstream report in their own words following the project's AI policy. - Tool: ruff ruff 0.17.1 - Rule: G010 (tool labels the fix: unknown, this fix reported as safe) - Oracle: fix-changes-behavior - Judge (Nemotron 3 Ultra, advisory): intended-change, severity low. The rule rewrites the deprecated `warn` method to `warning` to eliminate the DeprecationWarning, which is exactly the documented purpose. The stderr output changes from a deprecation warning to the actual log message 'test', demonstrating the fix works as intended. - Program: minimized from 5 to 3 lines ## Reproducer ```python import logging my_logger = logging.getLogger() my_logger.warn('test') ``` ## Commands ```sh python3 prog.py ruff check --preview --isolated --select G010 --fix prog.py python3 prog.py ``` ## Observed ``` stderr before: /w/prog.py:3: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead stderr after: test ``` ## Diff applied by the fix ```diff --- orig.py 2026-10-22 13:29:10.319709053 -0400 +++ fixed.py 2026-10-22 13:29:12.973753374 -0400 @@ -1,3 +1,3 @@ import logging my_logger = logging.getLogger() -my_logger.warn('test') +my_logger.warning('test') ``` ## Why the rewrite is not equivalent (model draft, verify before use) The original call to `warn` emits both the logged message "test" and a deprecation warning to stderr because Python’s logging module treats `warn` as a deprecated alias that triggers a warning when used. The rewritten call uses `warning`, which logs the same message but does not emit any deprecation warning. Since the deprecation warning is part of the program’s observable output (stderr), changing from `warn` to `warning` alters the program’s behavior, making the transformation not semantics-preserving despite preserving the intended log output. The fix incorrectly assumes functional equivalence without accounting for side effects like warnings. ## Upstream search Queries: "G010 fix", "ruff G010 warn method", "logging logger warning call", "deprecated warn to warning" - duplicate: https://github.com/astral-sh/ruff/issues/12295 same G010 rule rewriting logging.Logger.warn to warning - related: https://github.com/astral-sh/ruff/issues/7248 tracks flake8-logging rules including G010 but not the autofix behavior change - related: https://github.com/astral-sh/ruff/issues/2186 documents G010 alias PGH002 but not the autofix defect - related: https://github.com/astral-sh/ruff/issues/13673 about G rules not working with loguru, different logger library - duplicate: https://github.com/astral-sh/ruff/issues/17219 closed as duplicate of issue 12295 about logging.Logger.warn access - related: https://github.com/astral-sh/ruff/issues/28407 extends TRY401 for log levels, different rule - related: https://github.com/astral-sh/ruff/issues/15555 requests autofix for G rules including G010 - related: https://github.com/astral-sh/ruff/issues/4136 TRY400 flags log.error vs log.exception, different rule - related: https://github.com/astral-sh/ruff/issues/4692 feature request for G101 logging-extra-attr-clash - related: https://github.com/astral-sh/ruff/issues/21889 BLE001 false positive with logging.warning, different rule - related: https://github.com/astral-sh/ruff/issues/11031 G004 doesn't work with inline instantiated logger, different G rule - related: https://github.com/astral-sh/ruff/issues/11854 new rule for formatted string passed to logging module - related: https://github.com/astral-sh/ruff/issues/14221 warn about deprecated API usage, general deprecation detection - related: https://github.com/astral-sh/ruff/issues/1507 use banned-api for deprecation checks including warn->warning - related: https://github.com/astral-sh/ruff/issues/18349 warn about errors from deprecated rules - related: https://github.com/astral-sh/ruff/issues/9770 deprecation discussion for ANN001 and ANN002 rules
All hits - [github, open] No error on `logging.Logger.warn` access [G010] — https://github.com/astral-sh/ruff/issues/12295 - [github, open] Implement `flake8-logging` — https://github.com/astral-sh/ruff/issues/7248 - [github, open] Add support for rule aliasing — https://github.com/astral-sh/ruff/issues/2186 - [github, closed] unused-function-argument not silenced by prefixed underscore if variable name is "次" — https://github.com/astral-sh/ruff/issues/28721 - [github, closed] G rules seems not working with loguru. — https://github.com/astral-sh/ruff/issues/13673 - [github, closed] Ord violation panic when fixing file with nightly compiler — https://github.com/astral-sh/ruff/issues/12469 - [github, closed] Pack of fuzzer Autofix/Infinite loop errors [2] — https://github.com/astral-sh/ruff/issues/8402 - [github, closed] Rule RUF027 cause panic — https://github.com/astral-sh/ruff/issues/9895 - [github, closed] Fixed code unformatted — https://github.com/astral-sh/ruff/issues/8619 - [github, closed] Add option to disable preview warnings — https://github.com/astral-sh/ruff/issues/8620 - [tavily] Importing a logger circumvents "logging-f-string (G004)" · Issue #17219 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/17219 - [github, open] Add an extended version of TRY401 for all log levels — https://github.com/astral-sh/ruff/issues/28407 - [github, open] Autofix for flake8-logging-format (G) rules — https://github.com/astral-sh/ruff/issues/15555 - [github, open] TRY400 flags log.error() + raise/sys.exit() — https://github.com/astral-sh/ruff/issues/4136 - [github, open] Feature request: G101 logging-extra-attr-clash (or a new, similar rule) to detect (potentially) unsafe dict unpacking — https://github.com/astral-sh/ruff/issues/4692 - [github, open] Feature: Port Sonar's Python scanner checks — https://github.com/astral-sh/ruff/issues/4935 - [github, closed] Callable compared with is True not flagged — https://github.com/astral-sh/ruff/issues/25145 - [github, closed] BLE001 (blind-except): false positive when logging via `warning` — https://github.com/astral-sh/ruff/issues/21889 - [github, closed] Rule G004 doesn't work with inline instantiated logger — https://github.com/astral-sh/ruff/issues/11031 - [github, closed] Is it possible to auto-fix a multi-line string `format` call with a single-line string template? — https://github.com/astral-sh/ruff/issues/5531 - [tavily] New Rule: Formatted string passed to logging module PYL-W1203 · Issue #11854 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/11854 - [github, open] Warn if anything marked as deprecated is used — https://github.com/astral-sh/ruff/issues/14221 - [github, open] Preview: Prevent duplicate warnings for repeated selections — https://github.com/astral-sh/ruff/issues/7367 - [github, open] Use `banned-api` for deprecation checks in general — https://github.com/astral-sh/ruff/issues/1507 - [github, open] Ignoring `import-private-name (PLC2701)` for `_typeshed` import — https://github.com/astral-sh/ruff/issues/15295 - [github, open] D417 Argument descriptions only required if there is an "Args" section — https://github.com/astral-sh/ruff/issues/2310 - [github, open] Server doesn't detect ruff config for files not under working directory of server — https://github.com/astral-sh/ruff/issues/17944 - [github, open] Seeking improved pytest rules, as `flake8-pytest-style` doesn't align with best practices — https://github.com/astral-sh/ruff/issues/8796 - [github, open] Unified command for linting and formatting — https://github.com/astral-sh/ruff/issues/8232 - [github, closed] Duplication and inconsistency between pep585 annotation rules: UP006, UP035 — https://github.com/astral-sh/ruff/issues/15246 - [tavily] Warn about error being related to a deprecated rule · Issue #18349 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/18349 - [tavily] Deprecation of ANN 001 and 002 Discussion · Issue #9770 · astral-sh/ruff · GitHub — https://github.com/astral-sh/ruff/issues/9770