Repository navigation
Iterating over enum.Flag types ignores zero-valued in Python 3.11 #109633
Description
Bug report
Bug description:
In Python 3.10, you can iterate over enum.Enum and enum.Flag types to yield their values.
>>> import sys; print(sys.version)
3.10.12 | packaged by conda-forge | (main, Jun 23 2023, 22:40:32) [GCC 12.3.0]
>>> import enum
>>> class MyEnum(enum.Enum):
... A = 0
... B = 1
... C = 2
...
>>> list(MyEnum)
[<MyEnum.A: 0>, <MyEnum.B: 1>, <MyEnum.C: 2>]
>>> class MyFlag(enum.Flag):
... A = 0
... B = 1
... C = 2
...
>>> list(MyFlag)
[<MyFlag.A: 0>, <MyFlag.B: 1>, <MyFlag.C: 2>]In Python 3.11, the same is true for enum.Enum types, but the behavior seems to have changed for enum.Flag types. Now, iterating over the type only yields its nonzero values.
>>> import sys; print(sys.version)
3.11.5 | packaged by conda-forge | (main, Aug 27 2023, 03:34:09) [GCC 12.3.0]
>>> import enum
>>> class MyEnum(enum.Enum):
... A = 0
... B = 1
... C = 2
...
>>> list(MyEnum)
[<MyEnum.A: 0>, <MyEnum.B: 1>, <MyEnum.C: 2>]
>>> class MyFlag(enum.Flag):
... A = 0
... B = 1
... C = 2
...
>>> list(MyFlag)
[<MyFlag.B: 1>, <MyFlag.C: 2>] # Missing <MyFlag.A: 0> (!)CPython versions tested on:
3.10, 3.11
Operating systems tested on:
Linux
Activity
CharlieZhao95 commented on Sep 21, 2023
I bisected to here:
sobolevn commented on Sep 21, 2023
From the docs, I can say that now 0 is treated as more like a special value:
https://docs.python.org/3/library/enum.html#enum.Flag
Check how <Color: 0> is used all over the place.
The technical reason behind this is that now 0 does not get into _member_names_ here:
cpython/Lib/enum.py
Lines 313 to 319 in 712cb17
Because 0 is not a _is_single_bit member (it is explicit):
cpython/Lib/enum.py
Lines 93 to 98 in 712cb17
So, when we use __iter__ over _member_names_ zero-value is not there:
cpython/Lib/enum.py
Lines 790 to 794 in 712cb17
We need @ethanfurman :)
ethanfurman commented on Sep 21, 2023
It is more accurate to say that Enum and Flag iterate over the canonical values. For example:
class Color(Enum): RED = 1 GREEN = 2 BLUE = 3 ROJO = 1 VERDE = 2 AZUL = 3 list(Color) # RED, GREEN, BLUE class BlendColor(Flag): BLACK = 0 RED = 1 GREEN = 2 BLUE = 4 WHITE = RED | GREEN | BLUE list(BlendColor) # RED, GREEN, BLUEAliases have always been omitted from iteration, and flag values with no, or more than one, bit(s) set are considered aliases since Python 3.11 -- this was considered a bug-fix.
gmgunter commented on Sep 22, 2023
Oh I see. Thanks for the clarification, @ethanfurman.
Looking back over the docs now, they do pretty much convey everything that you've explained here, although some of the details are subtle. The only thing that I think isn't explicitly explained there is that zero-valued flags are considered aliases.
wimglenn commented on Jun 27, 2024
Why isn't F.f considered to be canonical?
ethanfurman commented on Jun 27, 2024
Because f is not a flag, it is a name for the absence of flags.
wimglenn commented on Jun 27, 2024
f shows up in F.__members__, but not in dir(F). Is that intended?
ethanfurman commented on Jun 28, 2024
Yes. dir(F) doesn't list aliases, but __members__ does (which also prevents aliases from being overridden -- i.e. F.f = 99 raises an AttributeError).
ClundXIII commented on Dec 5, 2024
Hi,
I do have a use case where I need both alias and elements of a flag. Is there a way to explicitly iterate over either only elements and only aliases that works in both old AND new version?
Leo1690 commented on Mar 21, 2025
@ClundXIII You can do this
from enum import IntFlag class Bla(IntFlag): X = 0 list(Bla.__members__.values())