os.path.ismount sometimes raises FileNotFoundError on Windows

[lazka]

BPO	28859
Nosy	@pfmoore, @tjguk, @zware, @zooba, @wm75, @lazka, @csabella, @dan1994, @szb512, @digglife, @AkechiShiro, @ankeshsaha
PRs	bpo-28859: Fix return value of ismount on Windows #19109

^{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 = None
created_at = <Date 2016-12-02.14:39:20.125>
labels = ['easy', 'type-bug', '3.8', '3.9', '3.7', 'OS-windows']
title = 'os.path.ismount sometimes raises FileNotFoundError on Windows'
updated_at = <Date 2020-05-23.20:05:59.911>
user = 'https://github.com/lazka'

bugs.python.org fields:

activity = <Date 2020-05-23.20:05:59.911>
actor = 'cheryl.sabella'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Windows']
creation = <Date 2016-12-02.14:39:20.125>
creator = 'lazka'
dependencies = []
files = []
hgrepos = []
issue_num = 28859
keywords = ['patch', 'easy', 'newcomer friendly']
message_count = 11.0
messages = ['282241', '357723', '361634', '362039', '362238', '364476', '364486', '365132', '365196', '365591', '369747']
nosy_count = 13.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'steve.dower', 'wolma', 'lazka', 'cheryl.sabella', 'Dan Arad', 'scic0', 'sdcards', 'akarei', 'AkechiShiro', 'ankeshsaha']
pr_nums = ['19109']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue28859'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']

[lazka]

It returns True for drives which don't exist and raises for paths starting with drives which don't exist.

>>> os.path.exists("C:\\")
True
>>> os.path.ismount("C:\\")
True
>>> os.path.ismount("C:\\doesnotexist")
False
>>> os.path.exists("F:\\")
False
>>> os.path.ismount("F:\\")
True
>>> os.path.ismount("F:\\doesnotexist")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\lazka\AppData\Local\Programs\Python\Python35\lib\ntpath.py", line 290, in ismount
    return path.rstrip(seps) == _getvolumepathname(path).rstrip(seps)
FileNotFoundError: [WinError 2] The system cannot find the file specified: 'F:\\doesnotexist'

[zooba]

Traditionally we handle exceptions in os.path.is* functions and return False.

[scic0]

I would like to take this issue as my first issue to start contributing to Python development.

[szb512]

I am going to think maybe it was the "os.path.ismount" command that is causing the issue. Does the file exist?

[zooba]

I am going to think maybe it was the "os.path.ismount" command that is causing the issue. Does the file exist?

If the file does not exist, it is definitely not a mount point. So the function should return False instead of raising an error.

[AkechiShiro]

Nishant Misra are you still working on this issue, if not could I take it from now on, as my first issue and contribution to Python?

[scic0]

Yes Lahfa Samy, you can take it up. I did not work on the issue.

[digglife]

I submitted a PR and get reviewed by @lazka. Is there anything I should do for pushing it to next step?

[zooba]

Reminding us on here is helpful (for me, anyway).

I just left a couple of suggestions to make sure we handle all the cases.

It's important when you change or add tests that you make sure the test fails without your fix - otherwise it might not be testing the fix!

[ankeshsaha]

s I have tried to workout a solution for the problem. Below is my observation and possible solution.

os.path.ismount("F:\\doesnotexist")

Exception occurs for the above line if the system fails to find both drive and the path that follows it.

A 'FileNotFoundError' exception is thrown. If we can handle this exception and return false for method ismount(), then problem can be resolved.

I changed the existing code ismount method and it is working.
Existing code=>
if _getvolumepathname:
return path.rstrip(seps) == _getvolumepathname(path).rstrip(seps)
else:
return False

Changed Code=>
if _getvolumepathname:
try:
return path.rstrip(seps) == _getvolumepathname(path).rstrip(seps)
except FileNotFoundError:
return False

Please check, if this solution is correct.

[csabella]

@steve.dower, please review the changes when you get a chance. Thanks!