python / python/mypy

[1.16 regression] Incompatible types error when using `Enum`s of a `NamedTuple`

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bug topic-enum
Dominant language
Python
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Description

Bug Report

Seeing this regression on mypy 1.16 with Enums of NamedTuples values.

Note: Enums of plain classes or dataclasses work as expected.

To Reproduce

https://mypy-play.net/?mypy=1.16.0&python=3.13&flags=strict&gist=2c5d8ca22757aee67d917d8fec20ad7f

from enum import Enum
from typing import NamedTuple

class Foo(NamedTuple):
    pass

class FooEnum(Foo, Enum):
    ITEM = Foo()

foo: Foo = FooEnum.ITEM  # works on 1.15 but not 1.16

Actual Behavior

error: Incompatible types in assignment (expression has type "FooEnum", variable has type "Foo")  [assignment]

Your Environment

  • Mypy version used: 1.16
  • Mypy command-line flags: defaults
  • Mypy configuration options from mypy.ini (and other config files): none
  • Python version used: 3.13

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 linked mypy-play reproduction and the embedded Foo/FooEnum snippet, comparing mypy 1.15 with 1.16 under Python 3.13. Trace the type-checking path for Enum members inheriting from NamedTuple. Done means the assignment is accepted again and regression coverage verifies that plain classes and dataclasses remain unaffected.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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