[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Paul Ganssle]

Paul Ganssle  added the comment:


New changeset 79d2e62c008446fbbc6f264bb8a30e2d38b6ff58 by Yaroslav Pankovych in 
branch 'master':
Added support for negative indexes to PurePath.parents (GH-21799)
https://github.com/python/cpython/commit/79d2e62c008446fbbc6f264bb8a30e2d38b6ff58


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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Paul Ganssle]

Change by Paul Ganssle :


--
dependencies:  -pathlib.PurePath.parents rejects negative indexes
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Paul Ganssle]

Paul Ganssle  added the comment:


New changeset 452058448335b39c784af9a047f9c4a1767c0b00 by Joshua Cannon in 
branch 'master':
bpo-35498: Added slice support to PathLib parents attribute. (GH-11165)
https://github.com/python/cpython/commit/452058448335b39c784af9a047f9c4a1767c0b00


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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Paul Ganssle]

Paul Ganssle  added the comment:

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.

--
nosy: +p-ganssle
versions: +Python 3.10 -Python 3.8

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Joshua Cannon]

Joshua Cannon  added the comment:

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.

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Julien Palard]

Julien Palard  added the comment:

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.

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nosy: +mdk

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Brett Cannon]

Change by Brett Cannon :


--
nosy: +brett.cannon

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

See also issue21041. 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.

--
dependencies: +pathlib.PurePath.parents rejects negative indexes
nosy: +serhiy.storchaka
versions: +Python 3.8 -Python 3.6

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Joshua Cannon]

Joshua Cannon  added the comment:

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).

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Joshua Cannon]

Change by Joshua Cannon :


--
keywords: +patch
pull_requests: +10401
stage:  -> patch review

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[issue35498] Parents objects in pathlib.Path don't support slices as __getitem__ arguments

[Joshua Cannon]

New submission from Joshua Cannon :

I would expect the following to work:
```
>>> import pathlib
>>> pathlib.Path.cwd().parents[0:1]
Traceback (most recent call last):
  File "", line 1, in 
  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.

--
components: Library (Lib)
messages: 331841
nosy: thejcannon
priority: normal
severity: normal
status: open
title: Parents objects in pathlib.Path don't support slices as __getitem__ 
arguments
type: enhancement
versions: Python 3.6

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