pathlib behave differ between OS

[MondWan]

BPO	41448
Nosy	@pfmoore, @ronaldoussoren, @tjguk, @ned-deily, @zware, @koobs, @zooba
Superseder	bpo-38671: pathlib.Path.resolve(strict=False) returns relative path on Windows if the entry does not exist

^{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 2020-07-31.14:24:54.900>
created_at = <Date 2020-07-31.09:28:43.963>
labels = ['OS-mac', '3.8', 'type-bug', '3.7', 'OS-windows']
title = 'pathlib behave differ between OS'
updated_at = <Date 2020-07-31.14:24:54.899>
user = 'https://bugs.python.org/MondWan'

bugs.python.org fields:

activity = <Date 2020-07-31.14:24:54.899>
actor = 'eryksun'
assignee = 'none'
closed = True
closed_date = <Date 2020-07-31.14:24:54.900>
closer = 'eryksun'
components = ['macOS', 'Windows', 'FreeBSD']
creation = <Date 2020-07-31.09:28:43.963>
creator = 'Mond Wan'
dependencies = []
files = []
hgrepos = []
issue_num = 41448
keywords = []
message_count = 6.0
messages = ['374632', '374635', '374637', '374638', '374639', '374640']
nosy_count = 8.0
nosy_names = ['paul.moore', 'ronaldoussoren', 'tim.golden', 'ned.deily', 'zach.ware', 'koobs', 'steve.dower', 'Mond Wan']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '38671'
type = 'behavior'
url = 'https://bugs.python.org/issue41448'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[MondWan]

I have tried 2 functions with different behavior across platform

# as_posix()

In linux platform, as_posix() cannot process window path nicely

• From linux + docker + python:3.8

Python 3.8.0 (default, Oct 17 2019, 05:36:36)
[GCC 8.3.0] on linux

>>> winPath = r'\workspace\xxx\test_fixture\user-restore-success.zip'
>>> posixPath = '/workspace/xxx/test_fixture/user-restore-success.zip'
>>> pWIN = pathlib.PurePath(winPath)
>>> pPOSIX = pathlib.PurePath(posixPath)
>>> pWIN.as_posix()
'\\workspace\\xxx\\test_fixture\\user-restore-success.zip'
>>> pPOSIX.as_posix()
'/workspace/xxx/test_fixture/user-restore-success.zip'

• From window + powershell + python3.6

Python 3.6.8 (tags/v3.6.8:3c6b436a57, Dec 24 2018, 00:16:47) [MSC v.1916 64 bit (AMD64)] on win32

>>> winPath = r'\workspace\xxx\test_fixture\user-restore-success.zip'
>>> posixPath = '/workspace/xxx/test_fixture/user-restore-success.zip'
>>> pWIN = pathlib.PurePath(winPath)
>>> pPOSIX = pathlib.PurePath(posixPath)
>>> pWIN.as_posix()
'/workspace/xxx/test_fixture/user-restore-success.zip'
>>> pPOSIX.as_posix()
'/workspace/xxx/test_fixture/user-restore-success.zip'

• From MAC

>>> winPath = '\\workspace\\xxx\\test_fixture\\user-restore-success.zip'
>>> posixPath = '/workspace/xxx/test_fixture/user-restore-success.zip'
>>> pWIN = pathlib.PurePath(winPath)
>>> pPOSIX = pathlib.PurePath(posixPath)
>>> pWIN.as_posix()
'\\workspace\\xxx\\test_fixture\\user-restore-success.zip'
>>> pPOSIX.as_posix()
'/workspace/xxx/test_fixture/user-restore-success.zip'

# resolve()

In window platform, resolve() returns absolute path only if such file is able to locate. Otherwise, it returns
relative path.

In Linux platform, resolve() returns absolute path anyway

• From linux

root@b4f03ed3003b:/var/run/lock# python
Python 3.8.0 (default, Oct 17 2019, 05:36:36)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pathlib
>>> p = pathlib.Path('no_exists')
>>> p.resolve()
PosixPath('/run/lock/no_exists')
>>> str(p.resolve())
'/run/lock/no_exits'

• From window

Python 3.6.8 (tags/v3.6.8:3c6b436a57, Dec 24 2018, 00:16:47) [MSC v.1916 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import pathlib
>>> p = pathlib.Path('README.md')
>>> p.resolve()
WindowsPath('C:/Users/xxx/PycharmProjects/yyy/README.md')
>>> str(p.resolve())
'C:\\Users\\xxx\\PycharmProjects\\yyy\\README.md'
>>> p = pathlib.Path('no_exists')
>>> p.resolve()
WindowsPath('no_exists')
>>> str(p.resolve())
'no_exists'

Also, I have spotted a ticket similar to this one

https://bugs.python.org/issue41357

[ronaldoussoren]

I'm not sure what you try to report.

PurePath(...) returns a PureWindowsPath on Windows and an PurePosixPath on other (unix-y) platforms. This explains the difference in behaviour you're seeing for as_posix().

[MondWan]

Let me clarify my expectation.

For as_posix()

• PureWindowsPath can translate both POSIX path, and WINDOW path to POSIX path via as_posix()

  • Therefore, I expect PurePosixPath can translate both platform path to POSIX path via as_posix()

• I just tried PurePosixPath() behave same between Window, and the docker.

  • I am sorry for showing misleading information

For resolve()

• In window platform, resolve() returns absolute path only if such file is able to locate. Otherwise, it returns
  relative path.

• In Linux platform, resolve() returns absolute path anyway

[MondWan]

Moreover, output from PurePosixPath.as_posix() is not that straightforward?

Please take a look below example from python3.6 + linux + docker

>>> winPath = r'\workspace\xxx\test_fixture\user-restore-success.zip'

>>> pWIN = pathlib.PureWindowsPath(winPath)
>>> pppFromWinPath = pathlib.PurePosixPath(winPath)
>>> pppFromPwp = pathlib.PurePosixPath(pWIN)

>>> pppFromWinPath.as_posix()
'\\workspace\\xxx\\test_fixture\\user-restore-success.zip'
>>> pppFromPwp.as_posix()
'\\/workspace/xxx/test_fixture/user-restore-success.zip'

• Construction PurePosixPath from rawString, as_posix() gives '\workspace\xxx\test_fixture\user-restore-success.zip'
• Construction PurePosixPath from PureWindowsPath, as_posix() gives '\/workspace/xxx/test_fixture/user-restore-success.zip'

[ronaldoussoren]

PureWindowsPath does not know about POSIX paths, it supports the two styles of directory separator that are valid on Windows: '/' and '\'.

PurePosixPath only supports the single stile of directory separator valid on POSIX systems: '/'.

On a Posix system backslash is a valid character in a file name and is NOT a directory separator.

The behaviour of Path.resolve() on Windows may or may not be a bug, the documentation is not quite clear. Personally I'd lean toward saying this is a bug, but I defer to a pathlib expert. Note that path.resolve(strict=True) should raise an error on both platforms when the path does not exists.