Difference in behaviour of PureWindowsPath in 3.12.0b2 with multiple slashes

[jnoortheen]

Bug report

I was trying to add Python3.12 beta 2 to the test suit of xonsh . The tests on Windows were failing because of the difference in behaviour of PureWindowsPath.

This can be reproduced like this

in Python 3.11

>>> from pathlib import PurePosixPath, PureWindowsPath
>>> PurePosixPath("///tmp")
PurePosixPath('/tmp')
>>> PureWindowsPath(r"\\\tmp")
PureWindowsPath('/tmp')

but the same in Python 3.12.0b2 would be giving different result

In [1]: from pathlib import PurePosixPath, PureWindowsPath
In [2]: PurePosixPath("///tmp")
Out[2]: PurePosixPath('/tmp')
In [3]: PureWindowsPath(r"\\\tmp")
Out[3]: PureWindowsPath('///tmp')

I've checked the changelog and this change of behaviour wasn't mentioned in it.

Your environment

• CPython versions tested on: 3.12.0b2
• Operating system and architecture: Windows 64bit

[arhadthedev]

git bisect points to 8af8f52 (gh-102003). @barneygale

How I performed the search, for reproducibility

• script

  git bisect start
  git bisect good v3.11.0
  git bisect bad main
  git bisect run .\gh-105881.cmd

• gh-105881.cmd:

  @echo off
  setlocal EnableDelayedExpansion
  
  git clean -fx -e gh-105881*
  call pcbuild\clean
  call pcbuild\build
  
  for /F "usebackq delims=" %%a IN (`call python.bat gh-105881.py`) do (
      if "%%a" == "PureWindowsPath('///tmp')" exit /b 1
  )

• gh-105881.py:

  from pathlib import PureWindowsPath
  print(repr(PureWindowsPath(r"\\\tmp")))

[barneygale]

In Python 3.12, all Windows paths beginning // or \\ are considered to be UNC paths, and so we don't remove leading slashes. In previous versions of Python the rules were more complex. More info here: #96290 (comment)

It's mentioned in the changelog (ctrl-f for "Fix handling of partial and invalid UNC drives in ntpath.splitdrive()") but the reST formatting of the entry is messed up. Will fix!

[jnoortheen]

Thanks for clarifying !