`Shutil.which` incosistent with windows's `where`

[alkuzad]

BPO	40592
Nosy	@pfmoore, @tjguk, @zware, @zooba, @alkuzad, @miss-islington, @peanutlord
PRs	bpo-40592: shutil.which will not return None anymore if ; is the last char in PATHEXT #20088 [3.9] bpo-40592: shutil.which will not return None anymore if ; is the last char in PATHEXT (GH-20088) #22912 [3.8] bpo-40592: shutil.which will not return None anymore if ; is the last char in PATHEXT (GH-20088) #22913

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-10-23.10:09:45.922>
created_at = <Date 2020-05-11.08:50:15.691>
labels = ['easy', '3.8', '3.9', '3.10', 'library', 'OS-windows']
title = "`Shutil.which` incosistent with windows's `where`"
updated_at = <Date 2020-10-23.21:38:08.966>
user = 'https://github.com/alkuzad'

bugs.python.org fields:

activity = <Date 2020-10-23.21:38:08.966>
actor = 'miss-islington'
assignee = 'none'
closed = True
closed_date = <Date 2020-10-23.10:09:45.922>
closer = 'steve.dower'
components = ['Library (Lib)', 'Windows']
creation = <Date 2020-05-11.08:50:15.691>
creator = 'alkuzad'
dependencies = []
files = []
hgrepos = []
issue_num = 40592
keywords = ['patch', 'easy', 'newcomer friendly']
message_count = 9.0
messages = ['368620', '368745', '368838', '379218', '379347', '379426', '379427', '379477', '379478']
nosy_count = 7.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'alkuzad', 'miss-islington', 'peanutlord']
pr_nums = ['20088', '22912', '22913']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue40592'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']

[alkuzad]

Shutil's which implementation does not work correctly when someone set's empty item in PATHEXT environment variable. Example:

set PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.RB;.RBW;

I'm not 100% sure how I got this in my PATHEXT config, I wasn't changing that so maybe some bugged uninstaller not removed it's extension correctly.

This makes things confusing as Windows will find correctly binary, but Python will return nothing, due to this part:

if any(cmd.lower().endswith(ext.lower()) for ext in pathext):
            files = [cmd]

pathext is initialized as pathext = os.environ.get("PATHEXT", "").split(os.pathsep), which ends producing '' as last element

Because any string ends with empty string (''), files list will have plain version added like git, which will then fail executable check.

Workaround is to use full name git.exe

Filtering out empty strings would fix that.

[zooba]

Sounds like a good opportunity for someone to make their first contribution.

Post a message if you'd like to work on this (and a test), and we can help get through the PR process.

[peanutlord]

@steve.dower I would really love to work on this and make my first contribution. Never did one, so I would some help doing this one :)

[peanutlord]

@steve.dower Added the changes in the PR - could you please re-check? Thank you!

[peanutlord]

@steve.dower Your advice did it, is fixed and green! :) Thank you again

[zooba]

New changeset da6f098 by Christopher Marchfelder in branch 'master':
bpo-40592: shutil.which will not return None anymore if ; is the last char in PATHEXT (GH-20088)
da6f098

[zooba]

Thanks for the contribution! Looking forward to your next one :)