3.11.1 Regression: namedtuple Enum values are cast to tuple

[Zannick]

Bug report

Between 3.11.0 and 3.11.1, Enums whose values are namedtuple objects have their values converted to tuple, which drops the field names we expect to be able to use, causing AttributeErrors. Test cases below create a namedtuple and an enum whose values are instances of that tuple. In the 3.11.1 case, referencing the enum value like NTEnum.NONE.value produces a tuple and not a namedtuple. In both cases, copy.copy preserves the namedtuple type.

It is not clear whether any item in the changelog or release notes references this change, nor could I quickly tell whether this was related to changes to address #93910.

Python 3.11.0 (main, Oct 24 2022, 18:26:48) [MSC v.1933 64 bit (AMD64)] on win32

>>> from enum import Enum
>>> from collections import namedtuple
>>> TTuple = namedtuple('TTuple', 'id a blist')
>>> class NTEnum(Enum):
...     NONE = TTuple(0, 0, [])
...     A = TTuple(1, 2, [4])
...     B = TTuple(2, 4, [0, 1, 2])
... 
...     
>>> NTEnum.NONE
<NTEnum.NONE: TTuple(id=0, a=0, blist=[])>
>>> NTEnum.NONE.value
TTuple(id=0, a=0, blist=[])
>>> [x.value for x in NTEnum]
[TTuple(id=0, a=0, blist=[]), TTuple(id=1, a=2, blist=[4]), TTuple(id=2, a=4, blist=[0, 1, 2])]
>>> import copy
>>> x = TTuple(0, 1, [7])
>>> x
TTuple(id=0, a=1, blist=[7])
>>> copy.copy(x)
TTuple(id=0, a=1, blist=[7])
>>> copy.deepcopy(x)
TTuple(id=0, a=1, blist=[7])
>>> NTEnum.NONE.value.blist
[]

Python 3.11.1 (tags/v3.11.1:a7a450f, Dec 6 2022, 19:58:39) [MSC v.1934 64 bit (AMD64)] on win32

>>> from enum import Enum
>>> from collections import namedtuple
>>> TTuple = namedtuple('TTuple', 'id a blist')
>>> class NTEnum(Enum):
...     NONE = TTuple(0, 0, [])
...     A = TTuple(1, 2, [4])
...     B = TTuple(2, 4, [0, 1, 2])
... 
...     
>>> NTEnum.NONE
<NTEnum.NONE: (0, 0, [])>
>>> NTEnum.NONE.value
(0, 0, [])
>>> [x.value for x in NTEnum]
[(0, 0, []), (1, 2, [4]), (2, 4, [0, 1, 2])]
>>> import copy
>>> x = TTuple(0, 1, [7])
>>> x
TTuple(id=0, a=1, blist=[7])
>>> copy.copy(x)
TTuple(id=0, a=1, blist=[7])
>>> copy.deepcopy(x)
TTuple(id=0, a=1, blist=[7])
>>> NTEnum.NONE.value.blist
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    NTEnum.NONE.value.blist
AttributeError: 'tuple' object has no attribute 'blist'

Your environment

• CPython versions tested on: 3.11.0, 3.11.1
• Operating system and architecture: win64 (amd64)
• 3.11.0 additionally tested on linux
• 3.11.0, 3.11.1 tested in IDLE

Linked PRs

• gh-100098: [Enum] insist on actual tuples, no subclasses, for auto #100099
• [3.11] gh-100098: [Enum] insist on actual tuples, no subclasses, for auto (GH-100099) #100102

[ethanfurman]

Thank you for the bug report. The fix will be in 3.11.2. If you need to use 3.11.1 you can inherit directly from TTuple:

>>> from enum import Enum
>>> from collections import namedtuple
>>> TTuple = namedtuple('TTuple', 'id a blist')
>>> class NTEnum(TTuple, Enum):
...     NONE = TTuple(0, 0, [])
...     A = TTuple(1, 2, [4])
...     B = TTuple(2, 4, [0, 1, 2])
... 
>>> NTEnum.A
<NTEnum.A: TTuple(id=1, a=2, blist=[4])>
>>> 
>>> NTEnum.A.id
1
>>> NTEnum.B.blist
[0, 1, 2]

On the up-side, the .value attribute is now a TTuple, and you can directly access the id, a, and blist attributes on the enum mebers; on the (possible) down-side, the enum member is directly comparable to tuples.

[tzaffi]

FYI, you can achieve equivalent functionality on python 3.11.1 for typing.NamedTuple using dataclasses as follows:

>>> from enum import Enum
>>> from dataclasses import dataclass
>>> 
>>> @dataclass
... class TTuple:
...     id: int
...     a: int
...     blist: list[int]
... 
>>> 
>>> class NTEnum(Enum):
...     NONE = TTuple(0, 0, [])
...     A = TTuple(1, 2, [4])
...     B = TTuple(2, 4, [0, 1, 2])
... 
>>> NTEnum.A
<NTEnum.A: TTuple(id=1, a=2, blist=[4])>
>>> NTEnum.A.value.id
1
>>> NTEnum.B.value.blist
[0, 1, 2]