pylint-dev/pylint

Using return value of a function that returns None is not always reported.

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#10,476 opened on 2025年8月5日

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False Negative 🦋Good first issueHacktoberfestHelp wanted 🙏Needs specification :closed_lock_with_key:

説明

Bug description

def f1(i: int) -> None:
    print(i)


def f2() -> None:
    r = f1(2)  # assignment-from-no-return
    if not r:
        print("error")
    if not f1(2):  # no error
        print("error")

Configuration

Command used

pylint experiments/type_test.py -E

Pylint output

experiments/type_test.py:6:4: E1111: Assigning result of a function call, where the function has no return (assignment-from-no-return)

Expected behavior

In the code snippet, line 6 will report an error, but line 9 doesn't. I'd expect to see an error on line 9, since the code essentially does the same thing. Not sure whether this is by design or a bug. If it's by design, feel free to change this issue to a feature request.

Pylint version

pylint 3.3.7
astroid 3.3.10
Python 3.13.5 (main, Jun 11 2025, 15:36:57) [Clang 17.0.0 (clang-1700.0.13.3)]

OS / Environment

MacOS 15.5

Additional dependencies

コントリビューターガイド

技術スタック
python
領域
developer experience
Issue 種別
bug
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。
2
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。
1-3 hours
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。
blocked
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
Python programmingFamiliarity with pylint internals
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。
70
調査方針
Start by examining the checker that raises 'assignment from no return' (likely in pylint/checkers/typecheck.py). Look at the detection logic: it currently catches assignments (e.g., `r = f1(2)`) but misses cases where the function call is used directly in a condition (e.g., `if not f1(2):`). Search for existing tests related to this warning and understand how the checker processes function call expressions. Consider extending the check to cover any expression that uses the return value of a None returning function, not just explicit assignments.