Cannot subclass from Protocol and Enum at the same time.

Bug report

Bug description:

x-ref: #119946 (comment)

When trying to create an Enum of classes that implement a certain Protocol, an unexpected 'Protocols cannot be instantiated' error is raised.

from enum import Enum, EnumType
from typing import Protocol

class Example(Protocol):
    def method(self) -> None: ...

class Impl(Example):
    def method(self) -> None: ...

Impl()  # OK

class CompatEnumType(type(Protocol), EnumType): ...

class ProtoEnum(Example, Enum, metaclass=CompatEnumType):
    impl = Impl()  # ERROR 'Protocols cannot be instantiated'

I have debugged this a bit and the issue is that _is_protocol is only set during Protocol.__init_subclass__, but Enum instantiates its members before this method is called.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

gh-149828: make Protocol compatible with Enum instantiation #149830

Closing as a dup of 119946 actually (since your PR targets another issue)

@picnixz

@picnixz Huh? This is a variant but different from that issue. My PR only fixes the variant described in #119946 (comment)

#119946 itself is solved by @sobolevn 's workaround (#119946 (comment))

EDIT: Oh dang I copied the wrong issue number in the PR title. The blurp-it uses #149828 though.

I fixed the incorrect issue number.

Ah ok! so I reopen this one!

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Cannot subclass from Protocol and Enum at the same time. #149828

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CPython versions tested on:

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Cannot subclass from Protocol and Enum at the same time. #149828

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

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picnixz commented on May 15, 2026

randolf-scholz commented on May 15, 2026

randolf-scholz commented on May 15, 2026

picnixz commented on May 15, 2026

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