false positive for type-hinted Enum class instance variable

[huwcbjones]

Bug description

As per https://mypy.readthedocs.io/en/stable/cheat_sheet_py3.html#classes, you can optionally declare instance variables in the class body. For normal classes, this is fine, but for Enums pylint raises a false positive

Define an enum with a type-hinted instance variable and you get an invalid name! 😞

class MyEnum(str, Enum):
    attr: int

    VALUE = "a", 1

    def __new__(cls, value, attr=None):
        obj = str.__new__(cls, value)
        obj._value_ = value
        obj.attr = attr
        return obj

Configuration

No response

Command used

pylint --disable=all --enable=invalid-name mwe.py

(pylint mwe.py also works, I just wanted to filter out the irrelavent messages)

Pylint output

************* Module mwe
mwe.py:5:4: C0103: Class constant name "attr" doesn't conform to UPPER_CASE naming style (invalid-name)

--------------------------------------------------------------------
Your code has been rated at 8.89/10

Expected behavior

No error

Pylint version

pylint 2.12.2/2.15.0
astroid 2.9.3/2.12.5
Python 3.9.1 (default, Mar 15 2021, 18:22:18)
[Clang 12.0.0 (clang-1200.0.32.27)]

OS / Environment

macOS

[huwcbjones]

From my quick peruse of the code, I believe that pylint will treat all Enum class variables as class constants, even if no value is assigned (the variable is for a type hint).
https://github.com/PyCQA/pylint/blob/880095c7266134a218e5f97075d1adeaa5b34b79/pylint/checkers/base/name_checker/checker.py#L459-L464

[mbyrnepr2]

Thanks for reporting. I think this is expected since Enum members are expected to be constants. Quoting from the docs:

Because Enums are used to represent constants we recommend using UPPER_CASE names for enum members, and will be using that style in our examples.

https://docs.python.org/3/library/enum.html

[Pierre-Sassoulas]

I'd also say it's working as intended.

[andrei-korshikov]

@mbyrnepr2 not quite so. VALUE (from the example above) is enum member, it is constant, and it should be upper case. But attr is not enum member, it is the attribute of enum member, so it is just ordinary attribute of instance, it's not class constant.

As reference example, look at the Planet from Python docs. They don't write self.MASS, but self.mass. So for type hinting we have to write mass: int with the lower case in the class Planet (Enum) body.

And here is my own example (that is why I've dug out this issue):

from enum import Enum

class Color(Enum):
    """Represents colors as (red, green, blue) tuples."""

    YELLOW      = 250, 250,   0
    KHAKI       = 250, 250, 125
    MAGENTA     = 250,   0, 250
    VIOLET      = 250, 125, 250
    CYAN        =   0, 250, 250
    AQUAMARINE  = 125, 250, 250

    # Class constant name "red" doesn't conform to UPPER_CASE naming style (invalid-name)
    # Class constant name "green" doesn't conform to UPPER_CASE naming style (invalid-name)
    # Class constant name "blue" doesn't conform to UPPER_CASE naming style (invalid-name)
    red: int
    green: int
    blue: int

    def __init__(self, red: int, green: int, blue: int) -> None:
        self.red   = red
        self.green = green
        self.blue  = blue

    @property
    def as_hex(self) -> str:
        """Get hex 'abcdef' representation for a color."""
        return f'{self.red:0{2}x}{self.green:0{2}x}{self.blue:0{2}x}'

@Pierre-Sassoulas I disagree with you:) @huwcbjones clearly showed to us that Pylint sees no difference between enum member and its instance variables. Is it possible to reopen the issue?

[mbyrnepr2]

Thank you @andrei-korshikov 👍 Completely agree with you.
I am working on fixing it 🎉

[DanielNoord]

@mbyrnepr2 In which PR has this been fixed? Might be good to link here.

[mbyrnepr2]

Two changes for this fix. A Pylint PR: #8905 and an astroid PR: pylint-dev/astroid#2263