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bpo-41517: do not allow Enums to be extended (GH-22271)

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fix bug that let Enums be extended via multiple inheritance
(cherry picked from commit 3064dbf5df)

Co-authored-by: Ethan Furman <ethan@stoneleaf.us>
This commit is contained in:
Miss Islington (bot) 2020-09-16 07:35:14 -07:00 • committed by GitHub
parent 6a39888c2c
commit 48f99250ff
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GPG key ID: 4AEE18F83AFDEB23
3 changed files with 18 additions and 5 deletions
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19
Lib/enum.py
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@ -123,10 +123,12 @@ class EnumMeta(type):
"""Metaclass for Enum"""
@classmethod
def __prepare__(metacls, cls, bases):
# check that previous enum members do not exist
metacls._check_for_existing_members(cls, bases)
# create the namespace dict
enum_dict = _EnumDict()
# inherit previous flags and _generate_next_value_ function
member_type, first_enum = metacls._get_mixins_(bases)
member_type, first_enum = metacls._get_mixins_(cls, bases)
if first_enum is not None:
enum_dict['_generate_next_value_'] = getattr(first_enum, '_generate_next_value_', None)
return enum_dict
@ -142,7 +144,7 @@ def __new__(metacls, cls, bases, classdict):
ignore = classdict['_ignore_']
for key in ignore:
classdict.pop(key, None)
member_type, first_enum = metacls._get_mixins_(bases)
member_type, first_enum = metacls._get_mixins_(cls, bases)
__new__, save_new, use_args = metacls._find_new_(classdict, member_type,
first_enum)
@ -401,7 +403,7 @@ def _create_(cls, class_name, names, *, module=None, qualname=None, type=None, s
"""
metacls = cls.__class__
bases = (cls, ) if type is None else (type, cls)
_, first_enum = cls._get_mixins_(bases)
_, first_enum = cls._get_mixins_(cls, bases)
classdict = metacls.__prepare__(class_name, bases)
# special processing needed for names?
@ -474,7 +476,14 @@ def _convert_(cls, name, module, filter, source=None):
return cls
@staticmethod
def _get_mixins_(bases):
def _check_for_existing_members(class_name, bases):
for chain in bases:
for base in chain.__mro__:
if issubclass(base, Enum) and base._member_names_:
raise TypeError("%s: cannot extend enumeration %r" % (class_name, base.__name__))
@staticmethod
def _get_mixins_(class_name, bases):
"""Returns the type for creating enum members, and the first inherited
enum class.
@ -499,7 +508,7 @@ def _find_data_type(bases):
elif not issubclass(base, Enum):
candidate = base
if len(data_types) > 1:
raise TypeError('too many data types: %r' % data_types)
raise TypeError('%r: too many data types: %r' % (class_name, data_types))
elif data_types:
return data_types[0]
else: