Upgrading to 10.0 on Windows breaks pip.exe

[BeatButton]

• Pip version: 9.0.3
• Python version: Python 3.6.5
• Operating system: Windows 10 x64 v1709

Description:

I'm trying to upgrade pip from 9.0.3 to 10.0.0. The minimum reproducible steps I've taken are:

1. Install Python 3.6.5 for all users in default location (C:\Program Files\Python36)
2. Start command prompt as administrator, run pip install -U pip
3. Afterwards, pip.exe is broken, but py -mpip is functional

What I've run:

Microsoft Windows [Version 10.0.16299.371]
(c) 2017 Microsoft Corporation. All rights reserved.

C:\Windows\system32>pip install -U pip
Collecting pip
  Using cached pip-10.0.0-py2.py3-none-any.whl
Installing collected packages: pip
  Found existing installation: pip 9.0.3
    Uninstalling pip-9.0.3:
      Successfully uninstalled pip-9.0.3
Exception:
Traceback (most recent call last):
  File "c:\program files\python36\lib\shutil.py", line 387, in _rmtree_unsafe
    os.unlink(fullname)
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\thebe\\AppData\\Local\\Temp\\pip-rcioww3v-uninstall\\program files\\python36\\scripts\\pip.exe'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\program files\python36\lib\site-packages\pip\basecommand.py", line 215, in main
  File "c:\program files\python36\lib\site-packages\pip\commands\install.py", line 342, in run
  File "c:\program files\python36\lib\site-packages\pip\req\req_set.py", line 795, in install
  File "c:\program files\python36\lib\site-packages\pip\req\req_install.py", line 767, in commit_uninstall
  File "c:\program files\python36\lib\site-packages\pip\req\req_uninstall.py", line 142, in commit
  File "c:\program files\python36\lib\site-packages\pip\_vendor\retrying.py", line 49, in wrapped_f
    return Retrying(*dargs, **dkw).call(f, *args, **kw)
  File "c:\program files\python36\lib\site-packages\pip\_vendor\retrying.py", line 212, in call
    raise attempt.get()
  File "c:\program files\python36\lib\site-packages\pip\_vendor\retrying.py", line 247, in get
    six.reraise(self.value[0], self.value[1], self.value[2])
  File "c:\program files\python36\lib\site-packages\pip\_vendor\six.py", line 686, in reraise
  File "c:\program files\python36\lib\site-packages\pip\_vendor\retrying.py", line 200, in call
    attempt = Attempt(fn(*args, **kwargs), attempt_number, False)
  File "c:\program files\python36\lib\site-packages\pip\utils\__init__.py", line 102, in rmtree
  File "c:\program files\python36\lib\shutil.py", line 494, in rmtree
    return _rmtree_unsafe(path, onerror)
  File "c:\program files\python36\lib\shutil.py", line 384, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  File "c:\program files\python36\lib\shutil.py", line 384, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  File "c:\program files\python36\lib\shutil.py", line 384, in _rmtree_unsafe
    _rmtree_unsafe(fullname, onerror)
  File "c:\program files\python36\lib\shutil.py", line 389, in _rmtree_unsafe
    onerror(os.unlink, fullname, sys.exc_info())
  File "c:\program files\python36\lib\site-packages\pip\utils\__init__.py", line 114, in rmtree_errorhandler
PermissionError: [WinError 5] Access is denied: 'C:\\Users\\thebe\\AppData\\Local\\Temp\\pip-rcioww3v-uninstall\\program files\\python36\\scripts\\pip.exe'

C:\Windows\system32>pip
Fatal error in launcher: Unable to create process using '""c:\program files\python36\python.exe"  "C:\Program Files\Python36\Scripts\pip.exe" -V'

C:\Windows\system32>py -mpip -V
pip 10.0.0 from C:\Program Files\Python36\lib\site-packages\pip (python 3.6)

[pradyunsg]

Hey @BeatButton!

This issue is a duplicate of #5223 -- if so, please close this to keep things easier to keep track of.

[BeatButton]

Whoops

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.