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.

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).

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.

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.

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.

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.

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

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