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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"PurePosixPath no longer correctly parses PureWindowsPath","articleBody":"# Bug report\r\n\r\nIn `pathlib` prior to Python 3.12, passing a `PureWindowsPath` to a `PurePosixPath` resulted in the Windows separator (`\\`) being converted to the POSIX separator (`/`). However, in the current main branch the backslashes are preserved in the `PurePosixPath` object.\r\n\r\nHere is an example which illustrates this:\r\n\r\n```pycon\r\nPython 3.12.0a7 (tags/v3.12.0a7:b861ba4, Apr  6 2023, 16:09:18) [Clang 10.0.0 ] on linux\r\nType \"help\", \"copyright\", \"credits\" or \"license\" for more information.\r\n\u003e\u003e\u003e import pathlib\r\n\u003e\u003e\u003e print(pathlib.PurePosixPath(pathlib.PureWindowsPath(r\"a\\b\\c\")))\r\na\\b\\c\r\n\u003e\u003e\u003e print(pathlib.PurePosixPath(pathlib.PureWindowsPath(r\"a\\b\\c\")).as_posix())\r\na\\b\\c \r\n```\r\n\r\n\r\n```pycon\r\nPython 3.11.2 (tags/v3.11.2:878ead1, Mar  9 2023, 16:26:59) [Clang 10.0.0 ] on linux\r\nType \"help\", \"copyright\", \"credits\" or \"license\" for more information.\r\n\u003e\u003e\u003e import pathlib\r\n\u003e\u003e\u003e print(pathlib.PurePosixPath(pathlib.PureWindowsPath(r\"a\\b\\c\")))\r\na/b/c\r\n\u003e\u003e\u003e print(pathlib.PurePosixPath(pathlib.PureWindowsPath(r\"a\\b\\c\")).as_posix())\r\na/b/c \r\n```\r\n\r\n(The behaviour is the same if using `PosixPath` or `WindowsPath` on the relevant platform; it's not specific to the \"pure\" variants.)\r\n\r\n-----\r\n\r\nBefore the recent refactoring of the module, passing one `Path` or `PurePath` object to another resulted in the `_parts` attribute being inspected. This was a list of the individual path elements (e.g. `['a', 'b', 'c']` for the path `a\\b\\c`).  The `_parts` attribute was removed in GH-102476 and replaced with `_tail`, but with slightly different semantics.\r\n\r\nThe current code replaces any `os.altsep`  in the path with `os.sep`, which for `WindowsPath` replaces `/` with `\\` but for `PosixPath` does nothing as there is no alternative separator. However, the following will produce a correct result:\r\n\r\n```pycon\r\nPython 3.12.0a7+ (heads/main:bd2ed06, Apr 19 2023, 15:27:47) [GCC 9.4.0] on linux\r\nType \"help\", \"copyright\", \"credits\" or \"license\" for more information.\r\n\u003e\u003e\u003e import pathlib\r\n\u003e\u003e\u003e pathlib.PurePosixPath._flavour.altsep = \"\\\\\"\r\n\u003e\u003e\u003e pathlib.PurePosixPath(pathlib.PureWindowsPath(r\"a\\b\\c\")).as_posix()\r\n'a/b/c'\r\n```\r\n\r\nThus I think the problem can be isolated to these lines here:\r\n\r\nhttps://github.com/python/cpython/blob/da2273fec7b1644786b9616592b53b04fdec4024/Lib/pathlib.py#L316-L324\r\n\r\n\r\n\r\n# Your environment\r\n\r\n- CPython versions tested on: 3.8, 3.11 and 3.12 (alpha 7 and HEAD)\r\n- Operating system and architecture: Ubuntu 20.04 and Windows 10\r\n\r\n\u003c!--\r\nYou can freely edit this text. Remove any lines you believe are unnecessary.\r\n--\u003e\r\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-104949\n* gh-104991\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/domdfcoding","@type":"Person","name":"domdfcoding"},"datePublished":"2023-04-19T15:05:52.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/103631/cpython/issues/103631"}