pathlib.Path('/').mkdir() raises wrong error type

[DanielLepage]

BPO	25803
Nosy	@pitrou, @serhiy-storchaka, @eryksun
PRs	bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) #805 bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True)… #806 bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True)… #807

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2017-03-24.19:50:35.993>
created_at = <Date 2015-12-05.03:48:12.568>
labels = ['3.7', 'type-bug', 'library']
title = "pathlib.Path('/').mkdir() raises wrong error type"
updated_at = <Date 2017-03-24.19:50:35.992>
user = 'https://bugs.python.org/DanielLepage'

bugs.python.org fields:

activity = <Date 2017-03-24.19:50:35.992>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2017-03-24.19:50:35.993>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-12-05.03:48:12.568>
creator = 'Daniel Lepage'
dependencies = []
files = []
hgrepos = []
issue_num = 25803
keywords = []
message_count = 7.0
messages = ['255916', '255956', '255958', '290100', '290105', '290112', '290113']
nosy_count = 4.0
nosy_names = ['pitrou', 'serhiy.storchaka', 'eryksun', 'Daniel Lepage']
pr_nums = ['805', '806', '807']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25803'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[DanielLepage]

pathlib.Path('/').mkdir() raises an IsADirectoryError instead of a FileExistsError.

[DanielLepage]

It looks like this is an OSX-specific behavior, and not a python problem:
$ mkdir .
mkdir: .: File exists
$ mkdir /
mkdir: /: Is a directory

[eryksun]

The mkdir method needs a fix similar to what was done for bpo-25583. For example, currently on Windows the exist_ok option doesn't handle the PermissionError raised when [accidentally] trying to create the root directory:

    >>> pathlib.Path('C:/').mkdir(exist_ok=True)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "C:\Program Files\Python 3.5\lib\pathlib.py", line 1199, in mkdir
        self._accessor.mkdir(self, mode)
      File "C:\Program Files\Python 3.5\lib\pathlib.py", line 371, in wrapped
        return strfunc(str(pathobj), *args)
    PermissionError: [WinError 5] Access is denied: 'C:\\'

[serhiy-storchaka]

I can't test on Windows and OSX but I suppose PR 805 fixes both issues.

[serhiy-storchaka]

New changeset af7b9ec by Serhiy Storchaka in branch 'master':
bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) (#805)
af7b9ec

[serhiy-storchaka]

New changeset 8c8785b by Serhiy Storchaka in branch '3.6':
bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True)… (#806)
8c8785b

[serhiy-storchaka]

New changeset 1fc1f8d by Serhiy Storchaka in branch '3.5':
bpo-25803: Avoid incorrect errors raised by Path.mkdir(exist_ok=True) (#805) (#807)
1fc1f8d