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philthompson10

opened on May 26, 2022

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The FlagBoundary added to enums in Python v3.11 has defaults that break compatibility with previous versions. Shouldn't the default initially be KEEP, with a deprecation warning that it will be changed in a future version?

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1. philthompson10

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on May 26, 2022
2. AlexWaygood

   added

   3.11only security fixesonly security fixes

   3.12only security fixesonly security fixes

   stdlibStandard Library Python modules in the Lib/ directoryStandard Library Python modules in the Lib/ directory

   on May 26, 2022
3. AlexWaygood

   assigned

   ethanfurman

   on May 26, 2022
4. The-Compiler commented on May 26, 2022

   

   The-Compiler

   on May 26, 2022

   Contributor

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   For some context: Python 3.11 and mixing of enum.IntFlag.

   Reproducer:

   import enum
   A = enum.IntFlag("A", {"x": 1})
   B = enum.IntFlag("B", {"y": 2})
   val = A.x | B.y
   print(val, type(val))

   $ python3.10 -c 'import enum; A = enum.IntFlag("A", {"x": 1}); B = enum.IntFlag("B", {"y": 2}); val = A.x | B.y; print(val, type(val))'
   A.B.y|x <enum 'A'>
   

   but

   $ python3.11 -c '...'
   3 <class 'int'>
   

   Relevant commit: 7aaeb2a ("bpo-38250: [Enum] single-bit flags are canonical (GH-24215)").
5. ethanfurman commented on May 26, 2022

   

   ethanfurman

   on May 26, 2022

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   Are you concerned that the repr() has changed, or that the result is no longer of type flag?
6. philthompson10 commented on May 26, 2022

   

   philthompson10

   on May 26, 2022

   Author

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   The change in type is the problem.
7. ethanfurman commented on May 26, 2022

   

   ethanfurman

   on May 26, 2022

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   Changing the default to KEEP make sense.

   Out of curiosity, and ignoring backwards compatibility, do you think the default for an IntFlag should be KEEP or EJECT?
8. philthompson10 commented on May 27, 2022

   

   philthompson10

   on May 27, 2022

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   I don't feel comfortable with the type being different depending on the values provided, so I don't like EJECT as a default as the behaviour might be too surprising.

   My use case is atypical. I am wrapping the enums of a C++ library and can't guarantee that the wrappers know about all the possible values that the library might provide. KEEP solves this problem. I have the same problem with Enum and IntEnum and have effectively implemented KEEP for those by providing them with an appropriate implementation of _missing_.

   Note that my original concern was about the lack of the usual deprecation cycle for a change in behaviour rather than the change itself.
9. ethanfurman

   added a commit that references this issue on May 27, 2022

   gh-93250: [Enum] Change IntEnum boundary to KEEP for backwards compat…

   70cfe56
10. miss-islington

    added a commit that references this issue on May 27, 2022

    pythongh-93250: [Enum] Change IntEnum boundary to KEEP for backwards …

    ba3cf54
11. ethanfurman

    added a commit that references this issue on May 27, 2022

    gh-93250: [Enum] Change IntEnum boundary to KEEP for backwards compat…

    647426d
12. ethanfurman commented on May 27, 2022

    

    ethanfurman

    on May 27, 2022

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    KEEP restored as the default, and likely to stay that way -- an early design decision was to persist the flag type for bit-wise operations. The exact flag type and behavior will depend on the left-most operand.

    Reacted by Freya Bruhin
13. ethanfurman

    closed this as completedon May 27, 2022
14. The-Compiler

    added a commit that references this issue on May 30, 2022

    Patch PyQt6 QUrl flag behavior for Python 3.11

    14c1593
15. The-Compiler

    added 5 commits that reference this issue on Jun 17, 2022

    Patch PyQt6 QUrl flag behavior for Python 3.11

    81094be

    Patch PyQt6 QUrl flag behavior for Python 3.11

    30012ca

    Patch PyQt6 QUrl flag behavior for Python 3.11

    b6a22a5

    Patch PyQt6 QUrl flag behavior for Python 3.11

    2538015

    Patch PyQt6 QUrl flag behavior for Python 3.11

    6b1f21d
16. The-Compiler

    added 3 commits that reference this issue on Aug 22, 2022

    Patch PyQt6 QUrl flag behavior for Python 3.11

    081fb3e

    Patch PyQt6 QUrl flag behavior for Python 3.11

    80d4ae3

    Patch PyQt6 QUrl flag behavior for Python 3.11

    4de0e90

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