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Inverted enum.Flag #107538

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Inverted enum.Flag#107538
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ethanfurman
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stdlibStandard Library Python modules in the Lib/ directorytype-bugAn unexpected behavior, bug, or error

Description

@GrafLearnt
GrafLearnt
opened on Aug 1, 2023

Bug report

Checklist

  • I am confident this is a bug in CPython, not a bug in a third-party project
  • I have searched the CPython issue tracker, and am confident this bug has not been reported before

A clear and concise description of the bug

Adding inverted option to enum.Flag brakes logic of enum.
I assume it caused by ambiguous implementation of bitwise NOT in Flag which processes ~value option different inside class scope and outside class scope unlike bitwise OR

import enum

class X(enum.Flag):
  a = enum.auto()
  b = enum.auto()
  c = a | b


assert list(X) == [X.a, X.b]
assert ~X.a == X.b
assert list(~X.a) == [X.b]


class Y(enum.Flag):
  a = enum.auto()
  b = enum.auto()
  c = a | b
  d = ~a  # this line brakes the code


assert list(Y) == [Y.a, Y.b]
assert ~Y.a == Y.b  # AssertionError
assert list(~Y.a) == [Y.b]  # ValueError: -2 is not a positive integer

Traceback:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1482, in __iter__
  yield from self._iter_member_(self._value_)
File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1359, in _iter_member_by_value_
  for val in _iter_bits_lsb(value & cls._flag_mask_):
File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 122, in _iter_bits_lsb
  raise ValueError('%r is not a positive integer' % original)
ValueError: -2 is not a positive integer

Your environment

  • CPython versions tested on: Clang 14.0.3 (clang-1403.0.22.14.1)
  • Operating system and architecture: 22.5.0 Darwin Kernel Version 22.5.0: Thu Jun 8 22:22:20 PDT 2023; root:xnu-8796.121.3~7/RELEASE_ARM64_T6000 arm64

Linked PRs

Activity

  1. GrafLearnt
    added
    type-bugAn unexpected behavior, bug, or error
    on Aug 1, 2023
  2. AlexWaygood
    added
    stdlibStandard Library Python modules in the Lib/ directory
    on Aug 1, 2023
  3. AlexWaygood
    assigned
    ethanfurman
    on Aug 1, 2023
  4. AlexWaygood
    added this to enum issueson Aug 1, 2023

  5. Eclips4 commented on Aug 1, 2023

    @Eclips4
    Eclips4
    on Aug 1, 2023
    Member

    Cannot reproduce on current main. Seems that this case fixed by #105542

  6. ethanfurman commented on Aug 1, 2023

    @ethanfurman
    ethanfurman
    on Aug 1, 2023
    Member

    It's not failing, and the first three work correctly, but Y.d should be an alias for Y.b, not -2.

  7. GrafLearnt commented on Aug 1, 2023

    @GrafLearnt
    GrafLearnt
    on Aug 1, 2023
    Author

    @ethanfurman may be you are right but I find following quite confusing:
    ~a changed while a remaining the same

    class X(enum.Flag):
    a = enum.auto()
    b = enum.auto()
    c = enum.auto()
    >>> list(X)
[<X.a: 1>, <X.b: 2>, <X.c: 4>]
>>> ~X.a
<X.b|c: 6>
>>> list(~X.a)
[<X.b: 2>, <X.c: 4>]
    class Y(enum.Flag):
    a = enum.auto()
    b = enum.auto()
    c = enum.auto()
    d = ~a
    >>> list(Y)
[<Y.a: 1>, <Y.b: 2>, <Y.c: 4>]
>>> ~Y.a
<Y.d: -2>
>>> list(~Y.a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1482, in __iter__
    yield from self._iter_member_(self._value_)
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1359, in _iter_member_by_value_
    for val in _iter_bits_lsb(value & cls._flag_mask_):
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 122, in _iter_bits_lsb
    raise ValueError('%r is not a positive integer' % original)
ValueError: -2 is not a positive integer

  8. ethanfurman commented on Aug 1, 2023

    @ethanfurman
    ethanfurman
    on Aug 1, 2023
    Member

    @GrafLearnt, in your latest example, d should be 6 (i.e. b|c). Thanks for the reminder, this will be a more involved fix than I was originally thinking.

  9. GrafLearnt commented on Aug 1, 2023

    @GrafLearnt
    GrafLearnt
    on Aug 1, 2023
    Author

    @ethanfurman d = b | c will work perfectly fine until someone add new member without adding it to d

  10. ethanfurman commented on Aug 1, 2023

    @ethanfurman
    ethanfurman
    on Aug 1, 2023
    Member

    Well, presumably, if they write d = b|c that's what they want; while d = ~a means every member that's not a.

  11. GrafLearnt commented on Aug 1, 2023

    @GrafLearnt
    GrafLearnt
    on Aug 1, 2023
    Author

    @ethanfurman
    I love it:

    class X(enum.Flag):
    a = enum.auto()
    b = enum.auto()
    c = enum.auto()
    >>> ~X.a
<X.b|c: 6>

    But this doesn't look correct to me:

    class Y(enum.Flag):
    a = enum.auto()
    b = enum.auto()
    c = enum.auto()
    d = ~a
    >>> ~Y.a
<Y.d: -2>

    Kindly ask to clarify if I am allowed to define inverted.
    It brakes iteration of ~Y.a
    Also I get following:

    >>> ~Y.b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1542, in __invert__
    self._inverted_ = self.__class__(self._flag_mask_ ^ self._value_)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 711, in __call__
    return cls.__new__(cls, value)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1136, in __new__
    raise exc
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1113, in __new__
    result = cls._missing_(value)
             ^^^^^^^^^^^^^^^^^^^^
  File "/opt/homebrew/Cellar/python@3.11/3.11.4_1/Frameworks/Python.framework/Versions/3.11/lib/python3.11/enum.py", line 1399, in _missing_
    raise ValueError(
ValueError: <flag 'Y'> invalid value -3
    given 0b1 01
  allowed 0b1 11

  12. ethanfurman commented on Aug 1, 2023

    @ethanfurman
    ethanfurman
    on Aug 1, 2023
    Member

    Defining ~a as a member is what is not working correctly.

    I believe that last error is fixed in 3.11.5.

  13. GrafLearnt commented on Aug 1, 2023

    @GrafLearnt
    GrafLearnt
    on Aug 1, 2023
    Author

    @ethanfurman is defining inverted restricted or will be fixed?

    Works fine in Python 3.10.12:

    >>> ~Y.b
<Y.c|a: 5>

  14. ethanfurman commented on Aug 1, 2023

    @ethanfurman
    ethanfurman
    on Aug 1, 2023
    Member

    Will be fixed.

  15. ethanfurman
    moved this to Todo in enum issueson Aug 1, 2023
  16. ethanfurman
    added a commit that references this issue on Jul 10, 2025

    gh-107538: [Enum] fix handling of inverted/negative values (GH-132273)

    49365bd
  17. ethanfurman
    closed this as completedon Jul 11, 2025
  18. github-project-automation
    moved this from Todo to Done in enum issueson Jul 11, 2025
  19. AndPuQing
    added a commit that references this issue on Jul 11, 2025

    pythongh-107538: [Enum] fix handling of inverted/negative values (pyt…

    87fdc0c
  20. Pranjal095
    added a commit that references this issue on Jul 12, 2025

    pythongh-107538: [Enum] fix handling of inverted/negative values (pyt…

    a3f1c85
  21. picnixz
    added a commit that references this issue on Jul 13, 2025

    pythongh-107538: [Enum] fix handling of inverted/negative values (pyt…

    337f8df
  22. taegyunkim
    added a commit that references this issue on Aug 4, 2025

    pythongh-107538: [Enum] fix handling of inverted/negative values (pyt…

    4ba9355
  23. Agent-Hellboy
    added a commit that references this issue on Aug 19, 2025

    pythongh-107538: [Enum] fix handling of inverted/negative values (pyt…

    07cf4c6
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