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Regression in IntFlag behaviour in f-string #86073

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rt121212121 mannequin opened this issue Oct 2, 2020 · 6 comments
Closed

Regression in IntFlag behaviour in f-string #86073

rt121212121 mannequin opened this issue Oct 2, 2020 · 6 comments
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@ethanfurman
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3.8 only security fixes 3.9 only security fixes 3.10 only security fixes stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@rt121212121
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Mannequin

rt121212121 mannequin commented Oct 2, 2020

BPO 41907
Nosy @warsaw, @ericvsmith, @ethanfurman, @miss-islington
PRs
  • bpo-41907: fix format() behavior for IntFlag #22497
  • [3.9] bpo-41907: [Enum] fix format() behavior for IntFlag (GH-22497) #23703
  • [3.8] bpo-41907: [Enum] fix format() behavior for IntFlag (GH-22497) #23704
    		•

    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = 'https://github.com/ethanfurman'
closed_at = <Date 2020-12-08.19:54:13.182>
created_at = <Date 2020-10-02.02:38:10.890>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = 'Regression in IntFlag behaviour in f-string'
updated_at = <Date 2020-12-08.19:54:13.181>
user = 'https://bugs.python.org/rt121212121'

    bugs.python.org fields:

    activity = <Date 2020-12-08.19:54:13.181>
actor = 'ethan.furman'
assignee = 'ethan.furman'
closed = True
closed_date = <Date 2020-12-08.19:54:13.182>
closer = 'ethan.furman'
components = ['Library (Lib)']
creation = <Date 2020-10-02.02:38:10.890>
creator = 'rt121212121'
dependencies = []
files = []
hgrepos = []
issue_num = 41907
keywords = ['patch']
message_count = 6.0
messages = ['377793', '377804', '377810', '382759', '382762', '382763']
nosy_count = 7.0
nosy_names = ['barry', 'eric.smith', 'eli.bendersky', 'ethan.furman', 'rt121212121', 'miss-islington', 'dom1310df']
pr_nums = ['22497', '23703', '23704']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue41907'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']
    @rt121212121
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    rt121212121 mannequin commented Oct 2, 2020

    An IntFlag member before 3.8.6 was converted to an integer in an f-string. After 3.8.6, the textual IntFlag class and member name are placed in the interpolated f-string instead of the integer.

    3.8.3: f"... {X.F} ..." where X.F = 1 << 4 will give "... 16 ..."
    3.8.5: Same
    3.8.6: f"... {X.F} ..." where X.F = 1 << 4 will give "... X.F ..."

    I have reproduced this on Linux using the version compiled and installed by pyenv, and on Windows using the 32-bit versions from the downloadable standalone installer.

    Now I have to locate and go through all my SQL statements and verify that they explicitly convert IntFlag values to integer to avoid the errors introduced by this regression.

    @rt121212121 rt121212121 mannequin added interpreter-core (Objects, Python, Grammar, and Parser dirs) 3.8 only security fixes type-bug An unexpected behavior, bug, or error labels Oct 2, 2020
    @dom1310df
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    dom1310df mannequin commented Oct 2, 2020

    I believe the regression is due to #58750 which "fixed" bpo-37479. The news entry states:

    "When Enum.__str__ is overridden in a derived class, the override will be used by Enum.__format__ regardless of whether mixin classes are present."

    .

    The change is in the __format__ method of Enum. It now checks if type(self).__str__ != Enum.__str__ and if True calls str(self). Because Flag defines its own __str__ method, the expression evaluates to True. I do not think this is the indented behaviour.

    In 3.8.5 str(self) was only called if _member_type_ is object.

    @ethanfurman
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    Thank you for the bug report.

    Another solution would be to subclass IntFlag and specify the __format__ method:

        from enum import IntFlag as _IntFlag
    class IntFlag(_IntFlag):
        def __format__(self, spec):
            return format(self.value, spec)

    @ethanfurman ethanfurman added 3.9 only security fixes 3.10 only security fixes labels Oct 2, 2020
    @ethanfurman ethanfurman self-assigned this Oct 2, 2020
    @ethanfurman ethanfurman added 3.9 only security fixes 3.10 only security fixes labels Oct 2, 2020
    @ethanfurman ethanfurman self-assigned this Oct 2, 2020
    @ethanfurman ethanfurman added stdlib Python modules in the Lib dir and removed interpreter-core (Objects, Python, Grammar, and Parser dirs) labels Oct 2, 2020
    @ethanfurman
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    New changeset 37440ee by Ethan Furman in branch 'master':
    bpo-41907: [Enum] fix format() behavior for IntFlag (GH-22497)
    37440ee

    @ethanfurman
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    New changeset 14eaa7d by Miss Islington (bot) in branch '3.9':
    bpo-41907: [Enum] fix format() behavior for IntFlag (GH-22497) (GH-23703)
    14eaa7d

    @ethanfurman
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    New changeset cbfcc67 by Miss Islington (bot) in branch '3.8':
    bpo-41907: [Enum] fix format() behavior for IntFlag (GH-22497) (GH-23704)
    cbfcc67

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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