[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Mitchell Young]

Mitchell Young  added the comment:

I am struggling with the same issue as Anthony. To provide a more direct 
response to Manjusaka's query:

python -c "import os; print(os.environ.get(\"PATHEXT\", 
\"\").split(os.pathsep))"
['.COM', '.EXE', '.BAT', '.CMD', '.VBS', '.VBE', '.JS', '.JSE', '.WSF', '.WSH', 
'.MSC']

Like Anthony, wondering if this should be it's own issue. Simply supporting 
paths with separators shouldn't, I think, lead to any of the ambiguities of 
matching a file exactly, without PATHEXT treatment.

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Anthony Sottile]

Anthony Sottile  added the comment:

sure, it's the standard PATHEXT (basically a fresh vm from modern.ie) -- the 
only reason I noticed this is I was reading the source: 
https://github.com/python/cpython/blob/5bbac8cbdf140ebce446ea4e7db2b20a5d7b8402/Lib/shutil.py#L1367-L1373



C:\Users\IEUser>echo %PATHEXT%
.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PY;.PYW

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Manjusaka]

Manjusaka  added the comment:

Hello Anthony

would you mind to execute this command on your PC?

python -c "import os; print(os.environ.get("PATHEXT", "").split(os.pathsep))"

and show the result about this code?

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Anthony Sottile]

Anthony Sottile  added the comment:

should I open a new issue for this, or is this an appropriate task to add to 
this discussion

shutil.which also doesn't apply `PATHEXT` when the path contains a directory 
separator

C:\Users\IEUser\astpretty>venv\Scripts\python --version
Python 3.7.5

C:\Users\IEUser\astpretty>venv\Scripts\python -c "import shutil; 
print(repr(shutil.which(r'venv\Scripts\python')))"
None

C:\Users\IEUser\astpretty>venv\Scripts\python -c "import shutil; 
print(repr(shutil.which(r'venv\Scripts\python.exe')))"
'venv\\Scripts\\python.exe'

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Роман Донченко]

Change by Роман Донченко :


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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Eryk Sun]

Eryk Sun  added the comment:

In a patch review [1] for issue 24505, I had a discussion with Toby Tobkin 
about extending the behavior of shutil.which() on Windows. This was to match 
the behavior of the CMD shell, including securing the search path via 
NeedCurrentDirectoryForExePath, searching for the exact filename, and 
implementing a real execute-access check. 

CMD won't directly execute a file that lacks execute access -- even a script or 
data file. We can implement this with a real implementation of os.access() that 
checks file security, for which there's an existing issue. (My previous 
suggestion to use CreateProcess and AssocQueryString to check for execute 
access was over the top. At the time I was thinking about building out support 
for a high-level shutil.execute, but it's out of scope here.)

Note that CMD will only try to execute an extensionless file if "." is in 
PATHEXT. (In the Windows file namespace, "name" and "name." are equivalent.) 
This obviously works for PE binaries, but we can also define an association for 
"." in the registy, which is useful for extensionless script files. Just 
associate "." files with a launcher that tries CreateProcess and falls back on 
a shebang line.

[1]: 
https://web.archive.org/web/20170619131224/http://bugs.python.org:80/review/24505/diff/16179/Lib/shutil.py

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Steve Dower]

Steve Dower  added the comment:

It certainly doesn't match "which" semantics, but given the F_OK and X_OK flags 
I can see cases where it ought not to. I'm not sure it does what it implies for 
those either though.

I can see uses for "find files according to 'which'" and "find executable files 
according to 'which'".

Either way, I don't see an easy way to change the semantics any earlier than 
3.8, so changing the target.

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versions: +Python 3.8 -Python 3.6

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Ryan McCampbell]

Ryan McCampbell  added the comment:

This is how windows looks up commands, as well as the built in "where" command. 
(Note that windows doesn't actually distinguish between "executable" files and 
just plain old files, so this could be confusing for UNIX users... a text file 
for instance will simply open in the default text editor when "executed" by the 
shell.)

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Paul Moore]

Paul Moore  added the comment:

On further reflection, I'm less sure that the proposed behaviour is the best 
option, but I do think this warrants further consideration.

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Paul Moore]

Paul Moore  added the comment:

I don't think this is expected behaviour. It's not documented what should 
happen in this case but the behaviour suggested by the OP (to search for the 
path as given, followed by [path+e for e in 
os.environ['PATHEXT'].split(os.pathsep)] seems reasonable to me.

The details and corner cases need thrashing out, which I don't have time to do 
right now, but the principle seems sound.

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Isn't this an expected behavior?

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

I am adding windows as a component during triaging since PATHEXT seems to be 
windows specific. Unfortunately, I couldn't verify this since I don't have 
windows system to check this against master so leaving it to 3.6.

Thanks

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nosy: +paul.moore, steve.dower, tim.golden, zach.ware

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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


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[issue31405] shutil.which doesn't find files without PATHEXT extension on Windows

[Ryan McCampbell]

New submission from Ryan McCampbell:

On windows, shutil.which does not match the semantics of built-in command 
lookup. If you pass the name of a script like foo.py and the PATHEXT variable 
doesn't include .py it will search for foo.py.exe, foo.py.bat, foo.py.cmd, etc. 
but not foo.py, which should be the first name checked.

--
components: Library (Lib)
messages: 301785
nosy: rmccampbell7
priority: normal
severity: normal
status: open
title: shutil.which doesn't find files without PATHEXT extension on Windows
type: behavior
versions: Python 3.6

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