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Clarify that atexit.unregister matches by equality, not identity #82243

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mdickinson opened this issue Sep 9, 2019 · 4 comments
Closed

Clarify that atexit.unregister matches by equality, not identity #82243

mdickinson opened this issue Sep 9, 2019 · 4 comments
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3.9 only security fixes 3.10 only security fixes 3.11 only security fixes docs Documentation in the Doc dir easy

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@mdickinson
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BPO 38062
Nosy @mdickinson, @miss-islington, @iritkatriel, @jdevries3133
PRs
  • bpo-38062: [doc] clarify that atexit uses equality comparisons internally. #26935
  • [3.10] bpo-38062: [doc] clarify that atexit uses equality comparisons internally. (GH-26935) #26956
  • [3.9] bpo-38062: [doc] clarify that atexit uses equality comparisons internally. (GH-26935) #26957
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    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 2021-06-29.18:22:49.469>
created_at = <Date 2019-09-09.08:51:28.823>
labels = ['easy', '3.11', '3.9', '3.10', 'docs']
title = 'Clarify that atexit.unregister matches by equality, not identity'
updated_at = <Date 2021-06-29.18:22:49.468>
user = 'https://github.com/mdickinson'

    bugs.python.org fields:

    activity = <Date 2021-06-29.18:22:49.468>
actor = 'iritkatriel'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-06-29.18:22:49.469>
closer = 'iritkatriel'
components = ['Documentation']
creation = <Date 2019-09-09.08:51:28.823>
creator = 'mark.dickinson'
dependencies = []
files = []
hgrepos = []
issue_num = 38062
keywords = ['patch', 'easy']
message_count = 4.0
messages = ['351363', '396748', '396751', '396752']
nosy_count = 5.0
nosy_names = ['mark.dickinson', 'docs@python', 'miss-islington', 'iritkatriel', 'jack__d']
pr_nums = ['26935', '26956', '26957']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue38062'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']
    @mdickinson
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    Suppose I have a class that looks like this:

        class A:
        def cleanup(self):
            print("Doing essential cleanup")

    and on an instance a = A(), I do: atexit.register(a.cleanup).

    Then it's not obvious from the documentation that an atexit.unregister(a.cleanup) will successfully undo the effect of the reigster call: the second a.cleanup is a different object from the first:

        >>> a = A()
    >>> clean1 = a.cleanup
    >>> clean2 = a.cleanup
    >>> clean1 is clean2
    False

    Luckily, though the two bound methods are different objects, they're equal:

        >>> clean1 == clean2
    True

    and from looking at the source, it's apparent that atexit.unregister compares by equality rather than identity, so everything works.

    It would be good to add a sentence to the documentation for atexit.unregister to clarify that this can be expected to work.

    @mdickinson mdickinson added docs Documentation in the Doc dir 3.7 (EOL) end of life 3.8 only security fixes labels Sep 9, 2019
    @iritkatriel iritkatriel added easy 3.9 only security fixes 3.10 only security fixes 3.11 only security fixes and removed 3.7 (EOL) end of life 3.8 only security fixes labels Jun 27, 2021
    @iritkatriel
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    New changeset 12803c5 by Jack DeVries in branch 'main':
    bpo-38062: [doc] clarify that atexit uses equality comparisons internally. (GH-26935)
    12803c5

    @iritkatriel
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    New changeset 08aa26e by Miss Islington (bot) in branch '3.10':
    bpo-38062: [doc] clarify that atexit uses equality comparisons internally. (GH-26935) (GH-26956)
    08aa26e

    @iritkatriel
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    New changeset 02859df by Miss Islington (bot) in branch '3.9':
    bpo-38062: [doc] clarify that atexit uses equality comparisons internally. (GH-26935) (GH-26957)
    02859df

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