ruff G010: fix changes program behavior

Hypothesis Nemotron 3 Super predicted to fire fired 1×

If `warn` is part of a larger identifier like `warning_prefix`, the replacement would produce `warning_prefixing`, causing a NameError or unintended variable reference.

Program

Output

(no stdout)
/w/prog.py:4: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead

(no stdout)
pre-fix

Judge Nemotron 3 Ultra advisory intended-change · low

The rule intentionally rewrites the deprecated `logger.warn` method to `logger.warning` to eliminate the DeprecationWarning, which is the documented purpose of the rule. The stderr output changes from showing a deprecation warning to showing only the logged message 'pre-fix', demonstrating the fix works as intended.

Explanation Nemotron 3 Super unverified

The original call to `logger.warn` produced a deprecation warning on stderr due to the outdated method name; replacing it with `logger.warning` eliminates that warning while preserving the same log output, so the program’s observable behavior changes by suppressing the deprecation message, even though the intended logging action remains identical. This alteration of side effects means the fix is not strictly semantics‑preserving.

Reproduce

file

prog.py (the before program)

minimized program

r1-p007.py

evidence sheet

r1-p007.md

regression fixture

r1-p007.py the minimized program with a header stating the observed change, for the tool's test suite

python3 prog.py
ruff check --preview --isolated --select G010 --fix prog.py
python3 prog.py

Upstream search GitHub issues Tavily Nemotron 3 Super + Ultra

G010 fix · ruff G010 warn method call · logging.warn deprecation replacement · method name change to warning

no duplicate or related report 31 hits triaged

Details

program

`warn` as substring in larger identifier

hazard

If `warn` is part of a larger identifier like `warning_prefix`, the replacement would produce `warning_prefixing`, causing a NameError or unintended variable reference.

oracle

stderr before: /w/prog.py:4: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead stderr after: pre-fix

run

2026-10-17T20-24-12-113Z-iye4-ruff-G010

--- orig.py	2026-10-17 16:24:30.005890406 -0400
+++ fixed.py	2026-10-17 16:24:30.271889712 -0400
@@ -4,5 +4,5 @@
 # Rule should ONLY replace .warn(...) -> .warning(...), NOT touch identifiers
 # So: logger.warn(warning_prefix + 'fix') -> logger.warning(warning_prefix + 'fix')
 # SAFE: no substring replacement in identifiers
-logger.warn(warning_prefix + 'fix')  # Correctly becomes .warning
+logger.warning(warning_prefix + 'fix')  # Correctly becomes .warning
 print(f'Prefix: {warning_prefix}')

# logging-warn (G010)

Derived from the **flake8-logging-format** linter.

Fix is always available.

## What it does
Checks for uses of `logging.warn` and `logging.Logger.warn`.

## Why is this bad?
`logging.warn` and `logging.Logger.warn` are deprecated in favor of
`logging.warning` and `logging.Logger.warning`, which are functionally
equivalent.

## Known problems

This rule detects uses of the `logging` module via a heuristic.
Specifically, it matches against:

- Uses of the `logging` module itself (e.g., `import logging; logging.info(...)`).
- Uses of `flask.current_app.logger` (e.g., `from flask import current_app; current_app.logger.info(...)`).
- Objects whose name starts with `log` or ends with `logger` or `logging`,
  when used in the same file in which they are defined (e.g., `logger = logging.getLogger(); logger.info(...)`).
- Imported objects marked as loggers via the [`lint.logger-objects`] setting, which can be
  used to enforce these rules against shared logger objects (e.g., `from module import logger; logger.info(...)`,
  when [`lint.logger-objects`] is set to `["module.logger"]`).

## Example
```python
import logging

logging.warn("Something happened")
```

Use instead:
```python
import logging

logging.warning("Something happened")
```

## Options
- `lint.logger-objects`

## References
- [Python documentation: `logging.warning`](https://docs.python.org/3/library/logging.html#logging.warning)
- [Python documentation: `logging.Logger.warning`](https://docs.python.org/3/library/logging.html#logging.Logger.warning)