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bpo-42851: [Enum] remove brittle __init_subclass__ support (GH-24154)

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Solution to support calls to `__init_subclass__` with members defined is too brittle and breaks with certain mixins.
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Ethan Furman 2021-01-07 13:17:55 -08:00 • committed by GitHub
parent 8643345bdb
commit a581a868d9
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3 changed files with 2 additions and 75 deletions
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31
Lib/enum.py
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@ -9,14 +9,6 @@ __all__ = [
]
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.
@ -227,22 +219,7 @@ class EnumMeta(type):
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
if bases:
bases = (_NoInitSubclass, ) + bases
enum_class = super().__new__(metacls, cls, bases, classdict, **kwds)
enum_class.__bases__ = enum_class.__bases__[1:] #or (object, )
else:
enum_class = super().__new__(metacls, cls, bases, classdict, **kwds)
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 = super().__new__(metacls, cls, bases, classdict, **kwds)
enum_class._member_names_ = [] # names in definition order
enum_class._member_map_ = {} # name->value map
enum_class._member_type_ = member_type
@ -354,9 +331,6 @@ class EnumMeta(type):
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):
@ -734,9 +708,6 @@ class Enum(metaclass=EnumMeta):
else:
return start
def __init_subclass__(cls, **kwds):
super().__init_subclass__(**kwds)
@classmethod
def _missing_(cls, value):
return None