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[3.8] bpo-41517: do not allow Enums to be extended (GH-22271) #22279

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Merged
merged 1 commit into from
Sep 16, 2020
Merged

[3.8] bpo-41517: do not allow Enums to be extended (GH-22271) #22279

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19 changes: 14 additions & 5 deletions Lib/enum.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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)

Expand Down Expand Up @@ -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?
Expand Down Expand Up @@ -480,7 +482,14 @@ def _convert(cls, *args, **kwargs):
return cls._convert_(*args, **kwargs)

@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.

Expand All @@ -505,7 +514,7 @@ 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:
Expand Down
3 changes: 3 additions & 0 deletions Lib/test/test_enum.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1000,6 +1000,9 @@ class MoreColor(Color):
cyan = 4
magenta = 5
yellow = 6
with self.assertRaisesRegex(TypeError, "EvenMoreColor: cannot extend enumeration 'Color'"):
class EvenMoreColor(Color, IntEnum):
chartruese = 7

def test_exclude_methods(self):
class whatever(Enum):
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2020-09-15-22-43-30.bpo-41517.sLBH7g.rst
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@@ -0,0 +1 @@
fix bug allowing Enums to be extended via multiple inheritance