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bpo-42567: [Enum] call __init_subclass__ after members are added #23714

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Merged
ethanfurman merged 2 commits into from
Dec 10, 2020
Merged

bpo-42567: [Enum] call __init_subclass__ after members are added #23714

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67b0d3d
call __init_subclass__ after members are added
ethanfurman Dec 9, 2020
d4be317
add news
ethanfurman Dec 9, 2020
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32 changes: 30 additions & 2 deletions Lib/enum.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,14 @@
]


class _NoInitSubclass:
"""
temporary base class to suppress calling __init_subclass__
"""
@classmethod
def __init_subclass__(cls, **kwds):
pass

def _is_descriptor(obj):
"""Returns True if obj is a descriptor, False otherwise."""
return (
Expand Down Expand Up @@ -134,7 +142,7 @@ def __prepare__(metacls, cls, bases):
enum_dict['_generate_next_value_'] = getattr(first_enum, '_generate_next_value_', None)
return enum_dict

def __new__(metacls, cls, bases, classdict):
def __new__(metacls, cls, bases, classdict, **kwds):
# an Enum class is final once enumeration items have been defined; it
# cannot be mixed with other types (int, float, etc.) if it has an
# inherited __new__ unless a new __new__ is defined (or the resulting
Expand Down Expand Up @@ -169,8 +177,22 @@ def __new__(metacls, cls, bases, classdict):
if '__doc__' not in classdict:
classdict['__doc__'] = 'An enumeration.'

# postpone calling __init_subclass__
if '__init_subclass__' in classdict and classdict['__init_subclass__'] is None:
raise TypeError('%s.__init_subclass__ cannot be None')
# remove current __init_subclass__ so previous one can be found with getattr
new_init_subclass = classdict.pop('__init_subclass__', None)
# create our new Enum type
enum_class = super().__new__(metacls, cls, bases, classdict)
if bases:
bases = (_NoInitSubclass, ) + bases
enum_class = type.__new__(metacls, cls, bases, classdict)
enum_class.__bases__ = enum_class.__bases__[1:] #or (object, )
else:
enum_class = type.__new__(metacls, cls, bases, classdict)
old_init_subclass = getattr(enum_class, '__init_subclass__', None)
# and restore the new one (if there was one)
if new_init_subclass is not None:
enum_class.__init_subclass__ = classmethod(new_init_subclass)
enum_class._member_names_ = [] # names in definition order
enum_class._member_map_ = {} # name->value map
enum_class._member_type_ = member_type
Expand Down Expand Up @@ -280,6 +302,9 @@ def __new__(metacls, cls, bases, classdict):
if _order_ != enum_class._member_names_:
raise TypeError('member order does not match _order_')

# finally, call parents' __init_subclass__
if Enum is not None and old_init_subclass is not None:
old_init_subclass(**kwds)
return enum_class

def __bool__(self):
Expand Down Expand Up @@ -632,6 +657,9 @@ def _generate_next_value_(name, start, count, last_values):
else:
return start

def __init_subclass__(cls, **kwds):
super().__init_subclass__(**kwds)

@classmethod
def _missing_(cls, value):
return None
Expand Down
73 changes: 73 additions & 0 deletions Lib/test/test_enum.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2117,6 +2117,43 @@ class ThirdFailedStrEnum(StrEnum):
class ThirdFailedStrEnum(StrEnum):
one = '1'
two = b'2', 'ascii', 9

def test_init_subclass(self):
class MyEnum(Enum):
def __init_subclass__(cls, **kwds):
super(MyEnum, cls).__init_subclass__(**kwds)
self.assertFalse(cls.__dict__.get('_test', False))
cls._test1 = 'MyEnum'
#
class TheirEnum(MyEnum):
def __init_subclass__(cls, **kwds):
super().__init_subclass__(**kwds)
cls._test2 = 'TheirEnum'
class WhoseEnum(TheirEnum):
def __init_subclass__(cls, **kwds):
pass
class NoEnum(WhoseEnum):
ONE = 1
self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
self.assertFalse(NoEnum.__dict__.get('_test1', False))
self.assertFalse(NoEnum.__dict__.get('_test2', False))
#
class OurEnum(MyEnum):
def __init_subclass__(cls, **kwds):
cls._test2 = 'OurEnum'
class WhereEnum(OurEnum):
def __init_subclass__(cls, **kwds):
pass
class NeverEnum(WhereEnum):
ONE = 'one'
self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
self.assertFalse(WhereEnum.__dict__.get('_test1', False))
self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
self.assertFalse(NeverEnum.__dict__.get('_test1', False))
self.assertFalse(NeverEnum.__dict__.get('_test2', False))


class TestOrder(unittest.TestCase):

Expand Down Expand Up @@ -2573,6 +2610,42 @@ def cycle_enum():
'at least one thread failed while creating composite members')
self.assertEqual(256, len(seen), 'too many composite members created')

def test_init_subclass(self):
class MyEnum(Flag):
def __init_subclass__(cls, **kwds):
super().__init_subclass__(**kwds)
self.assertFalse(cls.__dict__.get('_test', False))
cls._test1 = 'MyEnum'
#
class TheirEnum(MyEnum):
def __init_subclass__(cls, **kwds):
super(TheirEnum, cls).__init_subclass__(**kwds)
cls._test2 = 'TheirEnum'
class WhoseEnum(TheirEnum):
def __init_subclass__(cls, **kwds):
pass
class NoEnum(WhoseEnum):
ONE = 1
self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
self.assertFalse(NoEnum.__dict__.get('_test1', False))
self.assertFalse(NoEnum.__dict__.get('_test2', False))
#
class OurEnum(MyEnum):
def __init_subclass__(cls, **kwds):
cls._test2 = 'OurEnum'
class WhereEnum(OurEnum):
def __init_subclass__(cls, **kwds):
pass
class NeverEnum(WhereEnum):
ONE = 1
self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
self.assertFalse(WhereEnum.__dict__.get('_test1', False))
self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
self.assertFalse(NeverEnum.__dict__.get('_test1', False))
self.assertFalse(NeverEnum.__dict__.get('_test2', False))


class TestIntFlag(unittest.TestCase):
"""Tests of the IntFlags."""
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-12-08-22-43-35.bpo-42678.ba9ktU.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
`Enum`: call `__init_subclass__` after members have been added