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Parents objects in pathlib.Path don't support slices as __getitem__ arguments #79679

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thejcannon mannequin opened this issue Dec 14, 2018 · 8 comments
Closed

Parents objects in pathlib.Path don't support slices as __getitem__ arguments #79679

thejcannon mannequin opened this issue Dec 14, 2018 · 8 comments
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3.10 only security fixes stdlib Python modules in the Lib dir type-feature A feature request or enhancement

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@thejcannon
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thejcannon mannequin commented Dec 14, 2018

BPO 35498
Nosy @brettcannon, @serhiy-storchaka, @JulienPalard, @pganssle, @thejcannon
PRs
  • bpo-35498: Added slice support to PathLib parents attribute. #11165
    		•

    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 2020-11-20.15:46:16.796>
created_at = <Date 2018-12-14.16:55:17.375>
labels = ['type-feature', 'library', '3.10']
title = "Parents objects in pathlib.Path don't support slices as __getitem__ arguments"
updated_at = <Date 2020-11-23.20:06:38.266>
user = 'https://github.com/thejcannon'

    bugs.python.org fields:

    activity = <Date 2020-11-23.20:06:38.266>
actor = 'p-ganssle'
assignee = 'none'
closed = True
closed_date = <Date 2020-11-20.15:46:16.796>
closer = 'p-ganssle'
components = ['Library (Lib)']
creation = <Date 2018-12-14.16:55:17.375>
creator = 'thejcannon'
dependencies = []
files = []
hgrepos = []
issue_num = 35498
keywords = ['patch']
message_count = 8.0
messages = ['331841', '331854', '331923', '352283', '352331', '381453', '381485', '381695']
nosy_count = 5.0
nosy_names = ['brett.cannon', 'serhiy.storchaka', 'mdk', 'p-ganssle', 'thejcannon']
pr_nums = ['11165']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue35498'
versions = ['Python 3.10']
    @thejcannon
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    thejcannon mannequin commented Dec 14, 2018

    I would expect the following to work:

    >>> import pathlib
>>> pathlib.Path.cwd().parents[0:1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "...\Python36\lib\pathlib.py", line 593, in __getitem__
    if idx < 0 or idx >= len(self):
TypeError: '<' not supported between instances of 'slice' and 'int'

    Since pathlib documents parents as a sequence-type, and slicing a sequence is pretty standard behavior.

    @thejcannon thejcannon mannequin added stdlib Python modules in the Lib dir type-feature A feature request or enhancement labels Dec 14, 2018
    @thejcannon
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    thejcannon mannequin commented Dec 14, 2018

    If it is deemed a bug which needs to be fixed, I've gone ahead and attached the PR to fix it.

    CLA signage is pending approval at the company I work for, with most people out for the holidays (so it might be a day or two turnaround).

    @serhiy-storchaka
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    See also bpo-21041. First than add support for slices, we should make a decision about negative indices.

    In any case this is a new feature, which can be only added in the future 3.8 release.

    @serhiy-storchaka serhiy-storchaka added the 3.8 only security fixes label Dec 16, 2018
    @JulienPalard
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    Just commented on the related issue: https://bugs.python.org/issue21041#msg352281

    My question is: Why would you need to slice parents? parents already looks like the result of some slice.

    @thejcannon
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    thejcannon mannequin commented Sep 13, 2019

    Pretty much the same reason you would want to slice any other sequence. You want some range of values.

    top_most_3_dirs = myPath.parents[-3:]
grandparents_and_beyond = myPath.parents[1:]

    The same goes for negative indexes.

    @pganssle
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    One question I would have about this is that .parents is a lazily-calculated sequence, not a list or a tuple, so it's not immediately obvious what the return type of a slice would be. I don't think it makes sense to return, e.g. a _PathParents object with fewer parts, but I don't know if there's any traditional choice here, other than that the result of slicing Sequence is another Sequence.

    The PR returns a list, but I'm inclined to say we should return a tuple.

    @pganssle pganssle added 3.10 only security fixes and removed 3.8 only security fixes labels Nov 19, 2020
    @pganssle
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    New changeset 4520584 by Joshua Cannon in branch 'master':
    bpo-35498: Added slice support to PathLib parents attribute. (GH-11165)
    4520584

    @pganssle
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    New changeset 79d2e62 by Yaroslav Pankovych in branch 'master':
    Added support for negative indexes to PurePath.parents (GH-21799)
    79d2e62

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
    @KatherineTomkins KatherineTomkins mentioned this issue Aug 4, 2022
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