Some ntpath/posixpath functions unusable on foreign OS

The os.path docs intro includes:

Note: Since different operating systems have different path name conventions, there are several versions of this module in the standard library. The os.path module is always the path module suitable for the operating system Python is running on, and therefore usable for local paths. However, you can also import and use the individual modules if you want to manipulate a path that is always in one of the different formats. They all have the same interface:

• posixpath for UNIX-style paths
• ntpath for Windows paths

But we don't explain that some of the functions in ntpath and posixpath aren't suitable for usage on a "foreign" OS, e.g. that using ntpath.realpath() from POSIX is a bad idea.

These functions are safe because they do purely lexical work:

• basename
• commonpath
• commonprefix
• dirname
• isabs
• join
• normcase
• normpath
• split
• splitdrive
• splitroot
• splitext

These functions are probably unsafe because they rely on details of the host OS (e.g. via the os module):

• abspath
• exists
• lexists
• expanduser
• expandvars
• getatime
• getmtime
• getctime
• getsize
• isfile
• isdir
• isjunction
• islink
• ismount
• isdevdrive
• realpath
• relpath
• samefile
• sameopenfile
• samestat
• supports_unicode_filenames

Linked PRs

• gh-119772

issue にリンクされている os.path のドキュメントの概要から始め、字句的な関数とホスト依存の関数の一覧を確認してください。変更を加える前に、リンクされている PR gh-119772 を確認してください。ntpath と posixpath のどの関数が異なる OS 上でも安全で、どの関数がホスト OS に依存するのかをドキュメントで明確に説明できれば完了です。