Path.mkdir can get into a recursive error loop

[DanBuchoff]

BPO	29416
Nosy	@pfmoore, @tjguk, @zware, @eryksun, @zooba

^{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/zooba'
closed_at = <Date 2017-11-09.18:03:53.736>
created_at = <Date 2017-02-01.22:46:32.944>
labels = ['3.7', 'type-bug', 'library', 'OS-windows']
title = 'Path.mkdir can get into a recursive error loop'
updated_at = <Date 2017-11-09.18:03:53.735>
user = 'https://bugs.python.org/DanBuchoff'

bugs.python.org fields:

activity = <Date 2017-11-09.18:03:53.735>
actor = 'serhiy.storchaka'
assignee = 'steve.dower'
closed = True
closed_date = <Date 2017-11-09.18:03:53.736>
closer = 'serhiy.storchaka'
components = ['Library (Lib)', 'Windows']
creation = <Date 2017-02-01.22:46:32.944>
creator = 'Dan Buchoff'
dependencies = []
files = []
hgrepos = []
issue_num = 29416
keywords = []
message_count = 7.0
messages = ['286717', '286723', '286734', '286999', '287000', '287001', '287002']
nosy_count = 7.0
nosy_names = ['paul.moore', 'tim.golden', 'python-dev', 'zach.ware', 'eryksun', 'steve.dower', 'Dan Buchoff']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29416'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[DanBuchoff]

If a path has a non-existent anchor, Path.mkdir can get into a RecursionError as it tries to recursively create the parent. I expect a more sane error.

This is readily reproducible in Windows with Path('Z:').mkdir(parents=True)

Example execution:

Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 08:06:12) [MSC v.1900 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> from pathlib import Path
>>> Path('Z:').mkdir(parents=True)
Traceback (most recent call last):
  File "C:\Python36\lib\pathlib.py", line 1231, in mkdir
    self._accessor.mkdir(self, mode)
  File "C:\Python36\lib\pathlib.py", line 388, in wrapped
    return strfunc(str(pathobj), *args)
FileNotFoundError: [WinError 3] The system cannot find the path specified: 'Z:'

During handling of the above exception, another exception occurred:

...

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python36\lib\pathlib.py", line 1238, in mkdir
    self.parent.mkdir(parents=True)
  File "C:\Python36\lib\pathlib.py", line 1238, in mkdir
    self.parent.mkdir(parents=True)
  File "C:\Python36\lib\pathlib.py", line 1238, in mkdir
    self.parent.mkdir(parents=True)
  [Previous line repeated 989 more times]
  File "C:\Python36\lib\pathlib.py", line 1231, in mkdir
    self._accessor.mkdir(self, mode)
  File "C:\Python36\lib\pathlib.py", line 388, in wrapped
    return strfunc(str(pathobj), *args)
RecursionError: maximum recursion depth exceeded

[zooba]

Might be worth checking if this is resolved with bpo-29079, which is already in for 3.6.1.

[eryksun]

This case is similar to bpo-29079. It should only attempt to make the parent to handle ENOENT if self and self.parent aren't equal. Here's the snippet from Path.mkdir:

try:
    self._accessor.mkdir(self, mode)
except FileExistsError:
    if not exist_ok or not self.is_dir():
        raise
except OSError as e:
    if e.errno != ENOENT:
        raise
    self.parent.mkdir(parents=True)
    self._accessor.mkdir(self, mode)

[python-dev]

New changeset 8061d0967988 by Steve Dower in branch '3.5':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
https://hg.python.org/cpython/rev/8061d0967988

New changeset 3de58a54ed98 by Steve Dower in branch '3.6':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
https://hg.python.org/cpython/rev/3de58a54ed98

New changeset 09c018897fb3 by Steve Dower in branch 'default':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
https://hg.python.org/cpython/rev/09c018897fb3

[python-dev]

New changeset 661c40ba59855ebe4967424fcabd41be6f799137 by Steve Dower in branch 'master':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
661c40b

New changeset 77da63372461ddeb82dbfdef86e702e43e24e1da by Steve Dower in branch 'master':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
77da633

New changeset c05ffe646dc009c01365db917f0ca6b738fda69b by Steve Dower in branch 'master':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
c05ffe6

[python-dev]

New changeset 661c40ba59855ebe4967424fcabd41be6f799137 by Steve Dower in branch '3.6':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
661c40b

New changeset 77da63372461ddeb82dbfdef86e702e43e24e1da by Steve Dower in branch '3.6':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
77da633

[python-dev]

New changeset 661c40ba59855ebe4967424fcabd41be6f799137 by Steve Dower in branch '3.5':
Issue bpo-29416: Prevent infinite loop in pathlib.Path.mkdir
661c40b