pylint-dev/pylint

Expand to ``use-implicit-booleaness-not-len`` to catch `len(iterable) == 0` and `>0`

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#10,281 opened on 2025年3月17日

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False Negative 🦋Good first issueHacktoberfestNeeds decision :lock:

説明

Current problem

C1802 currently catches this

Examples 1&2 (currently caught by rule C1802)

fruits = ["orange", "apple"]
vegetables = []

if len(fruits):
    print(fruits)

if not len(vegetables):
    print(vegetables)

I come across the following sometimes as well (potentially in botched attempt to fix the the flagged violation above), which I think should be equally flagged as a violation.

Examples 3&4 (not caught by PLC1802)

fruits = ["orange", "apple"]
vegetables = []

if len(fruits) > 0:
    print(fruits)

if len(vegetables) == 0:
    print(vegetables)

Examples 5&6 (recommended formulation)

fruits = ["orange", "apple"]
vegetables = []

if fruits:
    print(fruits)

if not vegetables:
    print(vegetables)

Desired solution

Examples 3&4 to be flagged as well

Additional context

See our previous discussion on this issue.

コントリビューターガイド

技術スタック
python
領域
toolingdeveloper experience
Issue 種別
feature
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
1-2 days
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
active
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
Pythonpylint internalsAST knowledge
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
45
調査方針
The issue requests extending the existing rule C1802 (use implicit booleaness not len) to also flag cases like `len(iterable) > 0` and `len(iterable) == 0`. Start by examining the current implementation of the checker in pylint's source code, likely in the `checkers/` directory. Review the referenced discussion at https://github.com/astral sh/ruff/issues/16798#issuecomment 2729812152 for additional context. The solution involves adding AST pattern matching for these additional patterns in the rule's logic, similar to how the existing `len()` usage is detected.