python / python/mypy

Enum `@member` and `nonmember` mishandled in `Literal` types

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bug topic-enum
Dominant language
Python
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Description

Bug Report

typing.Literal is supposed to accept enum members and not non-members (such as methods or explicit nonmember attributes). mypy fails to enforce the latter and support the former.

To Reproduce

from enum import Enum, member, nonmember
from typing import Literal

class E(Enum):
    A = 1
    @member
    def B() -> None: ...
    C = member(lambda: None)
    D = nonmember(1)
    
    def meth(self) -> None: ...
    
a: Literal[E.A]  # OK, true negative
b: Literal[E.B]  # False positive: Parameter 1 of Literal[...] is invalid  [valid-type]
c: Literal[E.C]  # OK, true negative
d: Literal[E.D]  # False negative - `nonmember` shouldn't be allowed
meth: Literal[E.meth]  # OK, true positive: Parameter 1 of Literal[...] is invalid  [valid-type]

playground

Expected Behavior

  • The following should be accepted in Literal: E.A, E.B, E.C
  • The following should be rejected in Literal: E.D, E.meth

Actual Behavior

(line 7 is a different issue reported separately)

main.py:7: error: Method must have at least one argument. Did you forget the "self" argument?  [misc]
main.py:14: error: Parameter 1 of Literal[...] is invalid  [valid-type]
main.py:17: error: Parameter 1 of Literal[...] is invalid  [valid-type]

Your Environment

  • Mypy version used: 1.15.0 and current master
  • Mypy command-line flags: N/A
  • Mypy configuration options from mypy.ini (and other config files): N/A
  • Python version used: 3.12

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 by running the supplied Python 3.12 reproduction with mypy 1.15.0 or current master, then trace the Literal validation and enum-member handling involved in those diagnostics. Done means E.A, E.B, and E.C are accepted while E.D and E.meth are rejected.

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
45/100

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