`TypeError` when raising an exception inside the `__init__` method of an enum class

[Viicos]

Bug report

Bug description:

With #111815, any exception raised inside the __init__ method of an enum class ¹ is expected to be:

1. instantiable (not the case with Pydantic ValidationErrors, see Python 3.12 Enum Class Validated Initialization TypeError pydantic/pydantic#10593)
2. instantiable and expected to take a single argument.

cpython/Lib/enum.py

Lines 556 to 566 in 120b891

	try:
	exc = None
	classdict['_%s__in_progress' % cls] = True
	enum_class = super().__new__(metacls, cls, bases, classdict, **kwds)
	classdict['_%s__in_progress' % cls] = False
	delattr(enum_class, '_%s__in_progress' % cls)
	except Exception as e:
	# since 3.12 the line "Error calling __set_name__ on '_proto_member' instance ..."
	# is tacked on to the error instead of raising a RuntimeError
	# recreate the exception to discard
	exc = type(e)(str(e))

Meaning the following raises a TypeError instead of the expected MyValueError:

class MyValueError(ValueError):
    def __init__(self, t: str, v: int) -> None:
        self.t = t
        self.v = v

class ValidatedEnum(Enum):
    def __init__(self, value):
        raise MyValueError("", 1)


class MyValidatedEnum(ValidatedEnum):
    FOO = "foo"

# TypeError: MyValueError.__init__() missing 1 required positional argument: 'v'

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-125259: Fix error notes removal in enum initialization #125647
• [3.13] gh-125259: Fix error notes removal in enum initialization (GH-125647) #125858
• [3.12] gh-125259: Fix error notes removal in enum initialization (GH-125647) #125953

Footnotes

1. An example is documented as an example here. ↩