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gh-103479: [Enum] require __new__ to be considered a data type (GH-103495)

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a mixin must either have a __new__ method, or be a dataclass, to be interpreted as a data-type
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Ethan Furman 2023-04-13 08:31:03 -07:00 committed by GitHub
parent 2194071540
commit a6f95941a3
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3 changed files with 14 additions and 10 deletions
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8
Doc/howto/enum.rst
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@ -865,17 +865,19 @@ Some rules:
4. When another data type is mixed in, the :attr:`value` attribute is *not the 4. When another data type is mixed in, the :attr:`value` attribute is *not the
same* as the enum member itself, although it is equivalent and will compare same* as the enum member itself, although it is equivalent and will compare
equal. equal.
5. %-style formatting: ``%s`` and ``%r`` call the :class:`Enum` class's 5. A ``data type`` is a mixin that defines :meth:`__new__`, or a
:class:`~dataclasses.dataclass`
6. %-style formatting: ``%s`` and ``%r`` call the :class:`Enum` class's
:meth:`__str__` and :meth:`__repr__` respectively; other codes (such as :meth:`__str__` and :meth:`__repr__` respectively; other codes (such as
``%i`` or ``%h`` for IntEnum) treat the enum member as its mixed-in type. ``%i`` or ``%h`` for IntEnum) treat the enum member as its mixed-in type.
6. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`, 7. :ref:`Formatted string literals <f-strings>`, :meth:`str.format`,
and :func:`format` will use the enum's :meth:`__str__` method. and :func:`format` will use the enum's :meth:`__str__` method.
.. note:: .. note::
Because :class:`IntEnum`, :class:`IntFlag`, and :class:`StrEnum` are Because :class:`IntEnum`, :class:`IntFlag`, and :class:`StrEnum` are
designed to be drop-in replacements for existing constants, their designed to be drop-in replacements for existing constants, their
:meth:`__str__` method has been reset to their data types :meth:`__str__` method has been reset to their data types'
:meth:`__str__` method. :meth:`__str__` method.
When to use :meth:`__new__` vs. :meth:`__init__` When to use :meth:`__new__` vs. :meth:`__init__`

3
Lib/enum.py
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@ -967,6 +967,7 @@ class EnumType(type):
@classmethod @classmethod
def _find_data_type_(mcls, class_name, bases): def _find_data_type_(mcls, class_name, bases):
# a datatype has a __new__ method, or a __dataclass_fields__ attribute
data_types = set() data_types = set()
base_chain = set() base_chain = set()
for chain in bases: for chain in bases:
@ -979,7 +980,7 @@ class EnumType(type):
if base._member_type_ is not object: if base._member_type_ is not object:
data_types.add(base._member_type_) data_types.add(base._member_type_)
break break
elif '__new__' in base.__dict__ or '__init__' in base.__dict__: elif '__new__' in base.__dict__ or '__dataclass_fields__' in base.__dict__:
data_types.add(candidate or base) data_types.add(candidate or base)
break break
else: else:

13
Lib/test/test_enum.py
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@ -2737,10 +2737,10 @@ class TestSpecial(unittest.TestCase):
return 'ha hah!' return 'ha hah!'
class Entries(Foo, Enum): class Entries(Foo, Enum):
ENTRY1 = 1 ENTRY1 = 1
self.assertEqual(repr(Entries.ENTRY1), '<Entries.ENTRY1: ha hah!>')
self.assertTrue(Entries.ENTRY1.value == Foo(1), Entries.ENTRY1.value)
self.assertTrue(isinstance(Entries.ENTRY1, Foo)) self.assertTrue(isinstance(Entries.ENTRY1, Foo))
self.assertTrue(Entries._member_type_ is Foo, Entries._member_type_) self.assertTrue(Entries._member_type_ is Foo, Entries._member_type_)
self.assertTrue(Entries.ENTRY1.value == Foo(1), Entries.ENTRY1.value)
self.assertEqual(repr(Entries.ENTRY1), '<Entries.ENTRY1: ha hah!>')
# #
# check auto-generated dataclass __repr__ is not used # check auto-generated dataclass __repr__ is not used
# #
@ -2787,8 +2787,7 @@ class TestSpecial(unittest.TestCase):
DOG = ('medium', 4) DOG = ('medium', 4)
self.assertRegex(repr(Creature.DOG), "<Creature.DOG: .*CreatureDataMixin object at .*>") self.assertRegex(repr(Creature.DOG), "<Creature.DOG: .*CreatureDataMixin object at .*>")
def test_repr_with_init_data_type_mixin(self): def test_repr_with_init_mixin(self):
# non-data_type is a mixin that doesn't define __new__
class Foo: class Foo:
def __init__(self, a): def __init__(self, a):
self.a = a self.a = a
@ -2797,9 +2796,9 @@ class TestSpecial(unittest.TestCase):
class Entries(Foo, Enum): class Entries(Foo, Enum):
ENTRY1 = 1 ENTRY1 = 1
# #
self.assertEqual(repr(Entries.ENTRY1), '<Entries.ENTRY1: Foo(a=1)>') self.assertEqual(repr(Entries.ENTRY1), 'Foo(a=1)')
def test_repr_and_str_with_non_data_type_mixin(self): def test_repr_and_str_with_no_init_mixin(self):
# non-data_type is a mixin that doesn't define __new__ # non-data_type is a mixin that doesn't define __new__
class Foo: class Foo:
def __repr__(self): def __repr__(self):
@ -2911,6 +2910,8 @@ class TestSpecial(unittest.TestCase):
def test_init_exception(self): def test_init_exception(self):
class Base: class Base:
def __new__(cls, *args):
return object.__new__(cls)
def __init__(self, x): def __init__(self, x):
raise ValueError("I don't like", x) raise ValueError("I don't like", x)
with self.assertRaises(TypeError): with self.assertRaises(TypeError):