mirror of https://github.com/python/cpython
bpo-42567: [Enum] call __init_subclass__ after members are added (GH-23714)
When creating an Enum, type.__new__ calls __init_subclass__, but at that point the members have not been added. This patch suppresses the initial call, then manually calls the ancestor __init_subclass__ before returning the new Enum class.
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2a35137328
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32
Lib/enum.py
32
Lib/enum.py
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@ -9,6 +9,14 @@ __all__ = [
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]
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class _NoInitSubclass:
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"""
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temporary base class to suppress calling __init_subclass__
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"""
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@classmethod
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def __init_subclass__(cls, **kwds):
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pass
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def _is_descriptor(obj):
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"""
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Returns True if obj is a descriptor, False otherwise.
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@ -157,7 +165,7 @@ class EnumMeta(type):
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)
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return enum_dict
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def __new__(metacls, cls, bases, classdict):
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def __new__(metacls, cls, bases, classdict, **kwds):
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# an Enum class is final once enumeration items have been defined; it
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# cannot be mixed with other types (int, float, etc.) if it has an
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# inherited __new__ unless a new __new__ is defined (or the resulting
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@ -192,8 +200,22 @@ class EnumMeta(type):
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if '__doc__' not in classdict:
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classdict['__doc__'] = 'An enumeration.'
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# postpone calling __init_subclass__
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if '__init_subclass__' in classdict and classdict['__init_subclass__'] is None:
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raise TypeError('%s.__init_subclass__ cannot be None')
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# remove current __init_subclass__ so previous one can be found with getattr
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new_init_subclass = classdict.pop('__init_subclass__', None)
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# create our new Enum type
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enum_class = super().__new__(metacls, cls, bases, classdict)
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if bases:
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bases = (_NoInitSubclass, ) + bases
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enum_class = type.__new__(metacls, cls, bases, classdict)
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enum_class.__bases__ = enum_class.__bases__[1:] #or (object, )
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else:
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enum_class = type.__new__(metacls, cls, bases, classdict)
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old_init_subclass = getattr(enum_class, '__init_subclass__', None)
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# and restore the new one (if there was one)
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if new_init_subclass is not None:
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enum_class.__init_subclass__ = classmethod(new_init_subclass)
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enum_class._member_names_ = [] # names in definition order
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enum_class._member_map_ = {} # name->value map
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enum_class._member_type_ = member_type
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@ -305,6 +327,9 @@ class EnumMeta(type):
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if _order_ != enum_class._member_names_:
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raise TypeError('member order does not match _order_')
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# finally, call parents' __init_subclass__
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if Enum is not None and old_init_subclass is not None:
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old_init_subclass(**kwds)
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return enum_class
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def __bool__(self):
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@ -682,6 +707,9 @@ class Enum(metaclass=EnumMeta):
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else:
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return start
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def __init_subclass__(cls, **kwds):
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super().__init_subclass__(**kwds)
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@classmethod
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def _missing_(cls, value):
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return None
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@ -2117,6 +2117,43 @@ class TestEnum(unittest.TestCase):
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class ThirdFailedStrEnum(StrEnum):
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one = '1'
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two = b'2', 'ascii', 9
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def test_init_subclass(self):
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class MyEnum(Enum):
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def __init_subclass__(cls, **kwds):
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super(MyEnum, cls).__init_subclass__(**kwds)
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self.assertFalse(cls.__dict__.get('_test', False))
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cls._test1 = 'MyEnum'
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#
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class TheirEnum(MyEnum):
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def __init_subclass__(cls, **kwds):
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super().__init_subclass__(**kwds)
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cls._test2 = 'TheirEnum'
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class WhoseEnum(TheirEnum):
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def __init_subclass__(cls, **kwds):
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pass
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class NoEnum(WhoseEnum):
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ONE = 1
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self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
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self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
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self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
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self.assertFalse(NoEnum.__dict__.get('_test1', False))
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self.assertFalse(NoEnum.__dict__.get('_test2', False))
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#
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class OurEnum(MyEnum):
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def __init_subclass__(cls, **kwds):
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cls._test2 = 'OurEnum'
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class WhereEnum(OurEnum):
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def __init_subclass__(cls, **kwds):
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pass
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class NeverEnum(WhereEnum):
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ONE = 'one'
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self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
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self.assertFalse(WhereEnum.__dict__.get('_test1', False))
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self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
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self.assertFalse(NeverEnum.__dict__.get('_test1', False))
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self.assertFalse(NeverEnum.__dict__.get('_test2', False))
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class TestOrder(unittest.TestCase):
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@ -2573,6 +2610,42 @@ class TestFlag(unittest.TestCase):
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'at least one thread failed while creating composite members')
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self.assertEqual(256, len(seen), 'too many composite members created')
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def test_init_subclass(self):
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class MyEnum(Flag):
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def __init_subclass__(cls, **kwds):
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super().__init_subclass__(**kwds)
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self.assertFalse(cls.__dict__.get('_test', False))
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cls._test1 = 'MyEnum'
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#
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class TheirEnum(MyEnum):
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def __init_subclass__(cls, **kwds):
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super(TheirEnum, cls).__init_subclass__(**kwds)
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cls._test2 = 'TheirEnum'
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class WhoseEnum(TheirEnum):
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def __init_subclass__(cls, **kwds):
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pass
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class NoEnum(WhoseEnum):
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ONE = 1
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self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
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self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
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self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
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self.assertFalse(NoEnum.__dict__.get('_test1', False))
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self.assertFalse(NoEnum.__dict__.get('_test2', False))
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#
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class OurEnum(MyEnum):
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def __init_subclass__(cls, **kwds):
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cls._test2 = 'OurEnum'
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class WhereEnum(OurEnum):
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def __init_subclass__(cls, **kwds):
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pass
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class NeverEnum(WhereEnum):
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ONE = 1
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self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
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self.assertFalse(WhereEnum.__dict__.get('_test1', False))
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self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
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self.assertFalse(NeverEnum.__dict__.get('_test1', False))
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self.assertFalse(NeverEnum.__dict__.get('_test2', False))
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class TestIntFlag(unittest.TestCase):
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"""Tests of the IntFlags."""
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@ -0,0 +1 @@
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`Enum`: call `__init_subclass__` after members have been added
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