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Add __slots__ to ABC convenience class #74648

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aaronchall mannequin opened this issue May 24, 2017 · 4 comments
Closed

Add __slots__ to ABC convenience class #74648

aaronchall mannequin opened this issue May 24, 2017 · 4 comments
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3.7 (EOL) end of life stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@aaronchall
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aaronchall mannequin commented May 24, 2017

BPO 30463
Nosy @rhettinger, @cjw296, @serhiy-storchaka, @ilevkivskyi, @aaronchall
PRs
  • bpo-30463 ABC has empty __slots__, with unittest #1822
    		•

    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 2017-06-06.19:38:51.124>
created_at = <Date 2017-05-24.20:41:17.931>
labels = ['3.7', 'type-feature', 'library']
title = 'Add __slots__ to ABC convenience class'
updated_at = <Date 2019-11-16.01:14:18.818>
user = 'https://github.com/aaronchall'

    bugs.python.org fields:

    activity = <Date 2019-11-16.01:14:18.818>
actor = 'cjw296'
assignee = 'none'
closed = True
closed_date = <Date 2017-06-06.19:38:51.124>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2017-05-24.20:41:17.931>
creator = 'Aaron Hall'
dependencies = []
files = []
hgrepos = []
issue_num = 30463
keywords = []
message_count = 4.0
messages = ['294389', '294420', '295297', '356740']
nosy_count = 5.0
nosy_names = ['rhettinger', 'cjw296', 'serhiy.storchaka', 'levkivskyi', 'Aaron Hall']
pr_nums = ['1822']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue30463'
versions = ['Python 3.7']
    @aaronchall
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    aaronchall mannequin commented May 24, 2017

    We have __slots__ with other ABC's, see http://bugs.python.org/issue11333 and http://bugs.python.org/issue21421.

    There are no downsides to having empty slots on a non-instantiable class, but it does give the option of denying __dict__ creation for subclassers.

    The possibility of breaking is for someone using __slots__ but relying on __dict__ creation in a subclass - they will have to explicitly add "__dict__" to __slots__. Since we have added __slots__ to other ABC's,

    I will provide a PR soon on this. Diff should look like this (in Lib/abc.py):

    class ABC(metaclass=ABCMeta):
    """Helper class that provides a standard way to create an ABC using
    inheritance.
    """
- pass
+ __slots__ = ()

    (I also want to add a test for this, and ensure other ABC's also have this if they don't.)

    @rhettinger
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    This seems reasonable.

    @serhiy-storchaka
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    New changeset ff48739 by Serhiy Storchaka (Aaron Hall, MBA) in branch 'master':
    bpo-30463: Add an empty __slots__ to abc.ABC.
    ff48739

    @serhiy-storchaka serhiy-storchaka added 3.7 (EOL) end of life stdlib Python modules in the Lib dir labels Jun 6, 2017
    @serhiy-storchaka serhiy-storchaka added the type-feature A feature request or enhancement label Jun 6, 2017
    @cjw296
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    cjw296 commented Nov 16, 2019

    I will note that this means with:

    class BaseClass(ABC):
    pass


class MyDerivedClass(BaseClass):

    def __init__(self, thing):
        self.thing = thing

thing = MyDerivedClass()

    thing now has both __slots__ and, evidently, a dict. That's a bit weird and confusing.

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