[New-bugs-announce] [issue41889] enum: Mixin and int base class regression in 3.8.6

[puddly]

New submission from puddly <puddly3 at gmail.com>:

The following code worked in 3.8.5 but does not in 3.8.6 due to the fix for #39587:

```
import enum


class MyInt(int):
    def __new__(cls, value):
        return super().__new__(cls, value)

class HexMixin:
    def __repr__(self):
        return hex(self)

class MyIntEnum(HexMixin, MyInt, enum.Enum):
    pass


class Foo(MyIntEnum):
    TEST = 1

assert isinstance(Foo.TEST, MyInt)
assert repr(Foo.TEST) == "0x1"
```


In 3.8.6, the `Foo` enum itself fails to be created because `HexMixin` is now considered the member type instead of `MyInt`:

```
Traceback (most recent call last):
  File "enum_test.py", line 18, in <module>
    class Foo(MyIntEnum):
  File "/usr/local/Cellar/python at 3.8/3.8.6/Frameworks/Python.framework/Versions/3.8/lib/python3.8/enum.py", line 215, in __new__
    enum_member = __new__(enum_class)
TypeError: object.__new__(Foo) is not safe, use int.__new__()
```

----------
components: Library (Lib)
messages: 377692
nosy: barry, eli.bendersky, ethan.furman, puddly
priority: normal
severity: normal
status: open
title: enum: Mixin and int base class regression in 3.8.6
type: behavior
versions: Python 3.10, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41889>
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