Enum instance attributes are treated as class attributes

[SquidDev]

Version info

• Python: 3.12.3
• pytype: 48d1294

Details

Putting type annotations on attribute assignments inside an enum causes those attributes to be treated as Enum members, rather than attributes.

For instance, consider a my_enum.py:

import enum

class MyEnum(enum.Enum):
    def __init__(self, value: int):
        self.x: int = value

    X = 1
    Y = 2

And our entrypoint file:

from typing import assert_never

from my_enum import MyEnum


def consume(x: MyEnum) -> bool:
    match x:
        case MyEnum.X | MyEnum.Y:
            return True
        case y:
            assert_never(y)

Running pytype on this prints the following error:

testcase/main.py:11:13: error: in consume: Function typing.assert_never was called with the wrong arguments [wrong-arg-types]
         Expected: (arg: empty, ...)
  Actually passed: (arg: my_enum.MyEnum)

            assert_never(y)
            ~~~~~~~~~~~~~~~

However, if we replace the self.x: int = value with self.x = value, then this type checks successfully.

This does not happen when the enum is in the same file, and appears to be an issue with how things are serialised to a .pyi file. With the type annotation, we get the following interface file:

# (generated with --quick)

import enum
from typing import Literal

class MyEnum(enum.Enum):
    X: Literal[1]
    Y: Literal[2]
    x: int
    def __init__(self, value: int) -> None: ...

Without the type annotation, x is instead inferred to be x: Annotated[int, 'property'].