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Metaclasses interfere with __class_getitem__ #80173

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cdonovick mannequin opened this issue Feb 14, 2019 · 4 comments
Closed

Metaclasses interfere with __class_getitem__ #80173

cdonovick mannequin opened this issue Feb 14, 2019 · 4 comments
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3.7 (EOL) end of life docs Documentation in the Doc dir interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error

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@cdonovick
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cdonovick mannequin commented Feb 14, 2019

BPO 35992
Nosy @gvanrossum, @ilevkivskyi, @miss-islington, @cdonovick
PRs
  • bpo-35992: Use PySequence_GetItem only if sq_item is not NULL #11857
  • [3.7] bpo-35992: Use PySequence_GetItem only if sq_item is not NULL (GH-11857) #11910
    		•

    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 = None
closed_at = <Date 2019-02-17.23:35:10.511>
created_at = <Date 2019-02-14.06:14:12.765>
labels = ['interpreter-core', 'type-bug', '3.7', 'docs']
title = 'Metaclasses interfere with __class_getitem__'
updated_at = <Date 2019-02-17.23:35:10.510>
user = 'https://github.com/cdonovick'

    bugs.python.org fields:

    activity = <Date 2019-02-17.23:35:10.510>
actor = 'levkivskyi'
assignee = 'docs@python'
closed = True
closed_date = <Date 2019-02-17.23:35:10.511>
closer = 'levkivskyi'
components = ['Documentation', 'Interpreter Core']
creation = <Date 2019-02-14.06:14:12.765>
creator = 'donovick'
dependencies = []
files = []
hgrepos = []
issue_num = 35992
keywords = ['patch']
message_count = 4.0
messages = ['335497', '335521', '335790', '335791']
nosy_count = 5.0
nosy_names = ['gvanrossum', 'docs@python', 'levkivskyi', 'miss-islington', 'donovick']
pr_nums = ['11857', '11910']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue35992'
versions = ['Python 3.7']
    @cdonovick
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    cdonovick mannequin commented Feb 14, 2019

    OS:
    Debian testing

    python3 -VV:
    Python 3.7.2+ (default, Feb 2 2019, 14:31:48)
    [gcc 8.2.0]

    The following:

    class Meta(type): pass

class X(metaclass=Meta):
    def __class_getitem__(cls, key):
        return key

X[10]

    Results in

    TypeError: 'Meta' object does not support indexing

    However, PEP-560 specifically states that __class_getitem__ should be used as fall back for when a metaclass does not implement __getitem__.

    @cdonovick cdonovick mannequin added the 3.7 (EOL) end of life label Feb 14, 2019
    @cdonovick cdonovick mannequin assigned docspython Feb 14, 2019
    @cdonovick cdonovick mannequin added docs Documentation in the Doc dir interpreter-core (Objects, Python, Grammar, and Parser dirs) type-bug An unexpected behavior, bug, or error labels Feb 14, 2019
    @ilevkivskyi
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    Yes, I think this is a bug. Created a PR with a possible simple fix.

    @ilevkivskyi
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    New changeset ac28147 by Ivan Levkivskyi in branch 'master':
    bpo-35992: Use PySequence_GetItem only if sq_item is not NULL (GH-11857)
    ac28147

    @miss-islington
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    New changeset a7f929d by Miss Islington (bot) in branch '3.7':
    bpo-35992: Use PySequence_GetItem only if sq_item is not NULL (GH-11857)
    a7f929d

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