[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Eryk Sun]

Change by Eryk Sun :


--
resolution:  -> duplicate
stage:  -> resolved
status: open -> closed
superseder:  -> [Windows] OSError when testing whether pathlib.Path('*') exists

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Eryk Sun]

Change by Eryk Sun :


--
components: +Library (Lib)
versions:  -Python 3.6, Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Eryk Sun]

Eryk Sun  added the comment:

An alternative would be to add a "strict" parameter that defaults to False. In 
non-strict mode, map all OSError exceptions to a False return value. In strict 
mode, use _ignore_error(e) to determine whether to return False or propagate 
the exception. The question then is whether to add ERROR_INVALID_NAME (123) to 
_IGNORED_WINERRORS since the error means the name can never exist. On the other 
hand, ERROR_ACCESS_DENIED due to a permission error would be propagated in 
strict mode -- because the path's existence is unknown.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Steve Dower]

Steve Dower  added the comment:

Yeah, I think saying "return True if it provably exists and False if existence 
cannot be proven (and never raise)" is a good general rule for 
boolean-returning functions.

This definitely raises some edge cases where we can infer from certain error 
codes that a path exists, but I don't think it obliges us to prioritise fixing 
those in order to handle more obvious cases.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Paul Moore]

Paul Moore  added the comment:

So I guess the key question then is whether Path.exists() should trap 
exceptions and interpret them as "does not exist" (on all platforms, although 
it looks like the null character case in Unix has now been fixed). Which 
doesn't seem unreasonable, I guess.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Eryk Sun]

Eryk Sun  added the comment:

> "http:" isn't a valid drive letter, I'd imagine.

It's not a valid DOS drive, but that's not the problem. "http://w.org; is 
parsed as a relative path. The double slashes are replaced by a single 
backslash, and the Windows API tries to open the path relative to a handle for 
the current working directory. 

The issue is handling a path component named "http:". Some filesystems such as 
FAT32 reserve ":" as an invalid name character. Others such as NTFS and ReFS 
reserve ":" as the stream delimiter [1], and "http:" is not a valid stream 
name. I'm on the fence about how to handle names that the OS rejects as invalid 
in a boolean context (e.g. exists, isfile, etc). In one sense, returning False 
is reasonable because an invalid name cannot exist. But on the other hand, 
asking whether something that's invalid exists is a nonsense question that 
warrants an exception. That said, the issue has already been decided multiple 
times in favor of returning False, so at this point that's a pattern that 
should be consistently supported by the standard library.

Note that a filesystem may allow ":" as name character, such as the VirtualBox 
shared-folder filesystem redirector. But the latter brings up yet another 
twist. Adding a redirector into the device stack, and thus including the MUP 
(multiple UNC provider) device, brings along more path-parsing baggage. In this 
case a component name with ":" in it fails as bad syntax, which gets mapped to 
WinAPI ERROR_BAD_PATHNAME (161), and thus C ENOENT, and ultimately 
FileNotFoundError in Python. This is the case regardless of the filesystem. For 
example, let's use the SMB redirector to set the "//localhost/C$" share for the 
"C:" drive as the working directory:

>>> os.chdir('//localhost/C$')
>>> os.stat('http://w.org')
Traceback (most recent call last):
  File "", line 1, in 
FileNotFoundError: [WinError 161] The specified path is invalid: 
'http://w.org'

>>> Path('http://w.org').exists()
False

---

[1] https://docs.microsoft.com/en-us/windows/win32/fileio/file-streams

--
nosy: +eryksun

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Dominic Davis-Foster]

Dominic Davis-Foster  added the comment:

Paul's example with the embedded null no longer works on Python 3.8 as 
Path.exists returns False on ValueError (added in gh-7695)

Path.exists already ignores some Windows-specific errors, so I don't see why it 
shouldn't also ignore invalid paths which can't exist.

--
nosy: +domdfcoding2

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Paul Moore]

Paul Moore  added the comment:

"http:" isn't a valid drive letter, I'd imagine.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[gaborjbernat]

gaborjbernat  added the comment:

How come the link is invalid on Windows but valid on UNIX?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[Paul Moore]

Paul Moore  added the comment:

It's an invalid filename so it raises an exception.

You can get the same on Unix by using an invalid filename (embedded null):

>>> from pathlib import Path
>>> Path("/usr/\0").exists()
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib64/python3.7/pathlib.py", line 1356, in exists
    self.stat()
  File "/usr/lib64/python3.7/pathlib.py", line 1178, in stat
    return self._accessor.stat(self)
ValueError: embedded null byte

You need to be prepared for exceptions if you aren't sure you have a valid 
path. One thing that might be useful, I guess, is a `Path.is_valid()` function. 
But I don't know if all platforms have a way of asking the OS "is this a valid 
pathname?" So catching the exception is probably best.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue42855] pathlib.exists on Windows raises an exception on URL like/bad input

[gaborjbernat]

New submission from gaborjbernat :

❯ py -c "from pathlib import Path; Path('http://w.org').exists()"
Traceback (most recent call last):
  File "", line 1, in 
  File "C:\Python39\lib\pathlib.py", line 1407, in exists
self.stat()
  File "C:\Python39\lib\pathlib.py", line 1221, in stat
return self._accessor.stat(self)
OSError: [WinError 123] The filename, directory name, or volume label syntax is 
incorrect: 'http:\\w.org'

The above code returns correctly False on UNIX systems.

--
components: Windows
messages: 384569
nosy: gaborjbernat, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: pathlib.exists on Windows raises an exception on URL like/bad input
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com