pylint-dev/pylint

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

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#10,476 opened on Aug 5, 2025

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

Description

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

Contributor guide

Tech stack
python
Domain
developer experience
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
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blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Python programmingFamiliarity with pylint internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
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.