shutil.which should automatically look for file extension on Windows even when cmd includes path

[CarlGao4]

Bug report

Bug description:

In shutil.which, it will automatically add PATHEXT variable to the end of file and look for all those files:

cpython/Lib/shutil.py

Lines 1494 to 1515 in 7b55a95

	if sys.platform == "win32":
	# The current directory takes precedence on Windows.
	curdir = os.curdir
	if use_bytes:
	curdir = os.fsencode(curdir)
	if curdir not in path:
	path.insert(0, curdir)
	# PATHEXT is necessary to check on Windows.
	pathext_source = os.getenv("PATHEXT") or _WIN_DEFAULT_PATHEXT
	pathext = [ext for ext in pathext_source.split(os.pathsep) if ext]
	if use_bytes:
	pathext = [os.fsencode(ext) for ext in pathext]
	# See if the given file matches any of the expected path extensions.
	# This will allow us to short circuit when given "python.exe".
	# If it does match, only test that one, otherwise we have to try
	# others.
	if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
	files = [cmd]
	else:
	files = [cmd + ext for ext in pathext]

But before finding the executable in PATH, it will actually check whether the input cmd contains a directory:

cpython/Lib/shutil.py

Lines 1462 to 1468 in 7b55a95

	# If we're given a path with a directory part, look it up directly rather
	# than referring to PATH directories. This includes checking relative to the
	# current directory, e.g. ./script
	if os.path.dirname(cmd):
	if _access_check(cmd, mode):
	return cmd
	return None

But it won't automatically append the PATHEXT, which will fail to find some files.

Here are some results using the same paths with both PowerShell Get-Command and Python shutil.which

PS C:\> Get-Command ffmpeg

CommandType     Name                                               Version    Source
-----------     ----                                               -------    ------
Application     ffmpeg.exe                                         0.0.0.0    C:\Commands\ffmpeg\ffmpeg.exe

PS C:\> Get-Command C:\Commands\ffmpeg\ffmpeg.exe

CommandType     Name                                               Version    Source
-----------     ----                                               -------    ------
Application     ffmpeg.exe                                         0.0.0.0    C:\Commands\ffmpeg\ffmpeg.exe

PS C:\> Get-Command C:\Commands\ffmpeg\ffmpeg

CommandType     Name                                               Version    Source
-----------     ----                                               -------    ------
Application     ffmpeg.exe                                         0.0.0.0    C:\Commands\ffmpeg\ffmpeg.exe

Python 3.11.6 | packaged by conda-forge | (main, Oct  3 2023, 10:29:11) [MSC v.1935 64 bit (AMD64)]
Type 'copyright', 'credits' or 'license' for more information
IPython 8.14.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import shutil

In [2]: shutil.which("ffmpeg")
Out[2]: 'C:\\Commands\\ffmpeg\\ffmpeg.EXE'

In [3]: shutil.which(r"C:\Commands\ffmpeg\ffmpeg.exe")
Out[3]: 'C:\\Commands\\ffmpeg\\ffmpeg.exe'

In [4]: shutil.which(r"C:\Commands\ffmpeg\ffmpeg")  # Returns `None`

In [5]:

And in fact, all the paths above can be ran:

In [5]: import subprocess

In [6]: p = subprocess.Popen("ffmpeg -version", stdout=subprocess.PIPE)
   ...: p.wait()
Out[6]: 0

In [7]: p = subprocess.Popen(r"C:\Commands\ffmpeg\ffmpeg.exe -version", stdout=subprocess.PIPE)
   ...: p.wait()
Out[7]: 0

In [8]: p = subprocess.Popen(r"C:\Commands\ffmpeg\ffmpeg -version", stdout=subprocess.PIPE)
   ...: p.wait()
Out[8]: 0

In [9]: p = subprocess.Popen(r"C:\Commands\ffmpeg\ffmepg -version", stdout=subprocess.PIPE)  # A File does not exist
   ...: p.wait()
---------------------------------------------------------------------------
FileNotFoundError                         Traceback (most recent call last)
Cell In[9], line 1
----> 1 p = subprocess.Popen(r"C:\Commands\ffmpeg\ffmepg -version", stdout=subprocess.PIPE)
      2 p.wait()

File C:\ProgramData\miniconda3\envs\AI\Lib\subprocess.py:1026, in Popen.__init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags, restore_signals, start_new_session, pass_fds, user, group, extra_groups, encoding, errors, text, umask, pipesize, process_group)
   1022         if self.text_mode:
   1023             self.stderr = io.TextIOWrapper(self.stderr,
   1024                     encoding=encoding, errors=errors)
-> 1026     self._execute_child(args, executable, preexec_fn, close_fds,
   1027                         pass_fds, cwd, env,
   1028                         startupinfo, creationflags, shell,
   1029                         p2cread, p2cwrite,
   1030                         c2pread, c2pwrite,
   1031                         errread, errwrite,
   1032                         restore_signals,
   1033                         gid, gids, uid, umask,
   1034                         start_new_session, process_group)
   1035 except:
   1036     # Cleanup if the child failed starting.
   1037     for f in filter(None, (self.stdin, self.stdout, self.stderr)):

File C:\ProgramData\miniconda3\envs\AI\Lib\subprocess.py:1538, in Popen._execute_child(self, args, executable, preexec_fn, close_fds, pass_fds, cwd, env, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite, unused_restore_signals, unused_gid, unused_gids, unused_uid, unused_umask, unused_start_new_session, unused_process_group)
   1536 # Start the process
   1537 try:
-> 1538     hp, ht, pid, tid = _winapi.CreateProcess(executable, args,
   1539                              # no special security
   1540                              None, None,
   1541                              int(not close_fds),
   1542                              creationflags,
   1543                              env,
   1544                              cwd,
   1545                              startupinfo)
   1546 finally:
   1547     # Child is launched. Close the parent's copy of those pipe
   1548     # handles that only the child should have open.  You need
   (...)
   1551     # pipe will not close when the child process exits and the
   1552     # ReadFile will hang.
   1553     self._close_pipe_fds(p2cread, p2cwrite,
   1554                          c2pread, c2pwrite,
   1555                          errread, errwrite)

FileNotFoundError: [WinError 2] 

CPython versions tested on:

3.10, 3.11

Operating systems tested on:

Windows