StrEnum.__getitem__ raises TypeError

[injust]

Bug report

Bug description:

from enum import Enum, StrEnum, auto

class Foo(Enum):
    one = auto()
    two = auto()
    
class Bar(StrEnum):
    one = auto()
    two = auto()
    
names = ["one", "two"]

print([Foo[name] for name in names])
print(list(map(Foo.__getitem__, names)))

print([Bar[name] for name in names])
print(list(map(Bar.__getitem__, names)))  # TypeError: expected 1 argument, got 0

CPython versions tested on:

3.12, 3.13

Operating systems tested on:

macOS

[tom-pytel]

str class slots are overriding EnumType mapping for __getitem__ and others in StrEnum for certain uses.

>>> Foo.__getitem__
<bound method EnumType.__getitem__ of <enum 'Foo'>>

>>> Bar.__getitem__
<slot wrapper '__getitem__' of 'str' objects>

They work implicitly but not explicitly:

>>> Bar['one']
<Bar.one: 'one'>

>>> Bar.__getitem__('one')
Traceback (most recent call last):
  File "<python-input-19>", line 1, in <module>
    Bar.__getitem__('one')
    ~~~~~~~~~~~~~~~^^^^^^^
TypeError: expected 1 argument, got 0

>>> Bar.__getitem__(Bar, 'one')
Traceback (most recent call last):
  File "<python-input-20>", line 1, in <module>
    Bar.__getitem__(Bar, 'one')
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^
TypeError: descriptor '__getitem__' requires a 'str' object but received a 'EnumType'

Because Bar['one'] calls EnumType.__getitem__() and Bar.__getitem__('one') calls str.__getitem__(). This also applies to other magics like __contains__ or __len__:

>>> Bar.__contains__
<slot wrapper '__contains__' of 'str' objects>

>>> Bar.__len__
<slot wrapper '__len__' of 'str' objects>

>>> len(Bar)
2

>>> Bar.__len__()
Traceback (most recent call last):
  File "<python-input-22>", line 1, in <module>
    Bar.__len__()
    ~~~~~~~~~~~^^
TypeError: descriptor '__len__' of 'str' object needs an argument

>>> Bar.__len__(Bar)
Traceback (most recent call last):
  File "<python-input-23>", line 1, in <module>
    Bar.__len__(Bar)
    ~~~~~~~~~~~^^^^^
TypeError: descriptor '__len__' requires a 'str' object but received a 'EnumType'

>>> Bar.__len__('abc')
3

Quick hack fix, add the following to StrEnum to re-override methods overridden by str (if this is the desired behavior):

    # re-override methods overridden by str, see gh-128659
    __contains__ = classmethod(EnumType.__contains__)
    __getitem__ = classmethod(EnumType.__getitem__)
    __iter__ = classmethod(EnumType.__iter__)
    __len__ = classmethod(EnumType.__len__)

Before:

>>> Foo.__getitem__
<bound method EnumType.__getitem__ of <enum 'Foo'>>
>>> Bar.__getitem__
<slot wrapper '__getitem__' of 'str' objects>

After:

>>> Foo.__getitem__
<bound method EnumType.__getitem__ of <enum 'Foo'>>
>>> Bar.__getitem__
<bound method EnumType.__getitem__ of <enum 'Bar'>>
>>> Bar.__getitem__('one')
<Bar.one: 'one'>