astral-sh/ruff

Ruff --fix on SIM118 introducing TypeError

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#4,481 opened on May 17, 2023

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 (6 comments) (4 reactions) (0 assignees)Rust (47,527 stars) (2,088 forks)batch import
bughelp wantedtype-inference

Description

(Running a large repo through ruff --fix today, so might have a few of these tickets for you 😬)

Ruff --fix on the SIM118 rule is introducing a bug in our code (ruff=v0.0.267). The rule seems to flag any case where a keys() method is used. This works for dicts but doesn't work for classes with a keys() method but no __iter__.

Minimal example:

class Foo:
    def __init__(self) -> None:
        self._keys = [1,2,3]

    def keys(self) -> list[int]:
        return self._keys


foo = Foo()

for k in foo.keys():
    print(k)

Ruff error: SIM118 [*] Use k in foo instead of k in foo.keys()

ruff --fix converts this to for k in foo: which is a TypeError.

Thanks!

Contributor guide

Tech stack
pythonrust
Domain
tooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Python data model (duck typing)Rust programming fundamentals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Look at the implementation of the SIM118 rule in the Ruff codebase, likely under `crates/ruff/src/rules/` or `crates/ruff linter/src/rules/`. Identify the logic that triggers the `key in obj` suggestion and add a check to ensure the object is a dict or has an ` iter ` method. Review existing tests for SIM118 to understand the expected behavior. The fix involves modifying the rule to not flag objects that implement `keys()` but not ` iter `.