python / python/mypy

no error when `abstractmethod` and `property` decorators are used in the wrong order

Open
#12,895 0 comments 3 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

bug topic-descriptors topic-runtime-semantics
Dominant language
Python
Stars
20.6k
Forks
3.3k
PR merge metrics
PR metrics pending

Description

from abc import ABC, abstractmethod


class Foo(ABC):
    @abstractmethod
    @property
    def foo(self) -> int:
        ...

playground

this causes a runtime error, see https://github.com/python/cpython/issues/60471

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the playground example and compare mypy's behavior with the runtime failure described in the linked CPython issue. Trace how decorator combinations are analyzed, then add coverage for this snippet and verify that the incorrect order produces an appropriate diagnostic.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
42/100

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.