msg56644 - (view) |
Author: David Kågedal (d_kagedal) |
Date: 2007-10-22 12:04 |
When moving from Python 2.4 to Python 2.5, my program stopped working on
win32 because of a change in os.path.exists. I couldn't find any
description of the change, so I can only assume it's a bug.
The os.devnul variable contains the name of the "null file", which is
"/dev/null" on posix, and "nul" on win32. As I understand it, "NUL" is a
file that exists in every directory on win32.
Opening the "nul" file with open("nul", "r") works fine, but
os.path.exists("nul") returns False. In Python 2.4, it returns True.
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msg56645 - (view) |
Author: David Kågedal (d_kagedal) |
Date: 2007-10-22 12:23 |
It's called os.devnull, and nothing else.
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msg56652 - (view) |
Author: Facundo Batista (facundobatista) * |
Date: 2007-10-22 17:13 |
You migrated only of Python version, or also of windows installation?
I checked Py25 and Py23 in my Win 2k, and in both I have the same behaviour:
C:\Python23>python
Python 2.3.5 (#62, Feb 8 2005, 16:23:02) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.stat("nul")
Traceback (most recent call last):
File "<stdin>", line 1, in ?
OSError: [Errno 22] Invalid argument: 'nul'
>>> os.path.exists("nul")
False
>>>
I checked the os.stat() function because the documentation says that if
it gives an error, exists() will return False (and that this is how it's
implemented).
BTW, note that if you call to the GetFileAttributesEx() function of
kernel32.dll by yourself, it will give error for the "NUL" file, showing
that it actually does not exist.
Because of this, I'd say that current behaviour of os.exists() is ok,
but I want to know the answer of my question regarding your change
before closing this as not-a-bug.
Thanks!
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msg56674 - (view) |
Author: David Kågedal (d_kagedal) |
Date: 2007-10-23 07:09 |
I tried it on two different machines, and got two different answers:
conan$ /cygdrive/c/Python25/python -c 'import os.path; print
os.path.exists("nul")'
False
conan$ /cygdrive/c/Python24/python -c 'import os.path; print
os.path.exists("nul")'
False
conan$ /cygdrive/c/Python24/python -c 'import os; print os.stat("nul")'
Traceback (most recent call last):
File "<string>", line 1, in ?
OSError: [Errno 22] Invalid argument: 'nul'
conan$ /cygdrive/c/Python25/python -c 'import os; print os.stat("nul")'
Traceback (most recent call last):
File "<string>", line 1, in <module>
WindowsError: [Error 87] The parameter is incorrect: 'nul'
titti$ /cygdrive/c/Python24/python -c 'import os.path; print
os.path.exists("nul")'
True
titti$ /cygdrive/c/Python25/python -c 'import os.path; print
os.path.exists("nul")'
False
titti$ /cygdrive/c/Python24/python -c 'import os; print os.stat("nul")'
(33206, 0L, 3, 1, 0, 0, 0L, -1, -1, -1)
titti$ /cygdrive/c/Python25/python -c 'import os; print
os.stat("nul")'Traceback (most recent call last):
File "<string>", line 1, in <module>
WindowsError: [Error 87] The parameter is incorrect: 'nul'
I ran it from a cygwin prompt, but the pythons are native.
So you are correct that it doesn't work as I expected in Python 2.4
either on the "conan" host.. On "titti", there is a difference in how
os.path.exist works between 2.4 and 2.5. On "conan" there is actually
also a difference, but only in the exception raised by os.stat.
I don't know what the differences between these installation are.
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msg56684 - (view) |
Author: Kevin Dwyer (kdwyer) |
Date: 2007-10-23 17:37 |
I tried this under Python 2.3.3, 2.5.1 (native) and 2.3.4 (cygwin). The
operating system is Windows 2000 SP4.
C:\Python23>python
Python 2.3.3 (#51, Dec 18 2003, 20:22:39) [MSC v.1200 32 bit (Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
True
C:\Python25>python
Python 2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit
(Intel)] on
win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
False
$ python
Python 2.3.4 (#1, Jun 13 2004, 11:21:03)
[GCC 3.3.1 (cygming special)] on cygwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import os.path
>>> print os.path.exists('nul')
True
So there does seem to be a change in behaviour at 2.5.
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msg56692 - (view) |
Author: Kevin Dwyer (kdwyer) |
Date: 2007-10-23 20:56 |
Ok, it seems that Python 2.5 implements two new functions
Py_GetFileAttributesExA and Py_GetFileAttributesExW in posixmodule.c
within the #ifdef MS_WINDOWS block that may return
ERROR_INVALID_PARAMETER to os.stat, which will percolate WindowsError up
to os.exists():
In both functions we find:
static BOOL WINAPI
Py_GetFileAttributesExA(LPCSTR pszFile,
GET_FILEEX_INFO_LEVELS level,
LPVOID pv)
{
BOOL result;
LPWIN32_FILE_ATTRIBUTE_DATA pfad = pv;
/* First try to use the system's implementation, if that is
available and either succeeds to gives an error other than
that it isn't implemented. */
check_gfax();
if (gfaxa) {
result = gfaxa(pszFile, level, pv);
if (result || GetLastError() != ERROR_CALL_NOT_IMPLEMENTED)
return result;
}
/* It's either not present, or not implemented.
Emulate using FindFirstFile. */
if (level != GetFileExInfoStandard) {
SetLastError(ERROR_INVALID_PARAMETER);
return FALSE;
...
static BOOL WINAPI
Py_GetFileAttributesExW(LPCWSTR pszFile,
GET_FILEEX_INFO_LEVELS level,
LPVOID pv)
{
BOOL result;
LPWIN32_FILE_ATTRIBUTE_DATA pfad = pv;
/* First try to use the system's implementation, if that is
available and either succeeds to gives an error other than
that it isn't implemented. */
check_gfax();
if (gfaxa) {
result = gfaxw(pszFile, level, pv);
if (result || GetLastError() != ERROR_CALL_NOT_IMPLEMENTED)
return result;
}
/* It's either not present, or not implemented.
Emulate using FindFirstFile. */
if (level != GetFileExInfoStandard) {
SetLastError(ERROR_INVALID_PARAMETER);
return FALSE;
...
I'm neither a C nor a win32api programmer - can anyone explain the
purpose of this code?
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msg56733 - (view) |
Author: Martin v. Löwis (loewis) * |
Date: 2007-10-25 04:01 |
The purpose of Py_GetFileAttributesEx* is to wrap GetFileAttributesEx,
on systems where it doesn't exist (Windows 95 in particular). If it
doesn't exist, it is emulated; if it exists, it is directly called.
|
msg56734 - (view) |
Author: Martin v. Löwis (loewis) * |
Date: 2007-10-25 04:05 |
As Facundo found out, the behavior of os.path.exists is fairly
irrelevant here, as that functions is trivial. What really matters is
whether os.stat succeeds for NUL. Can those users for whom it succeeds
please report what Windows versions they are using, and what precisely
the stat result for NUL is (and perhaps also for CON, PRN, etc)?
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msg56735 - (view) |
Author: Martin v. Löwis (loewis) * |
Date: 2007-10-25 05:21 |
Please disregard Cygwin Python for this discussion. It (probably) uses
the stat implementation from cygwin1.dll, which may work differently
from Cygwin release to Cygwin release.
|
msg56795 - (view) |
Author: Facundo Batista (facundobatista) * |
Date: 2007-10-26 17:07 |
>>> import os.path
>>> os.path.exists("con")
False
>>> os.path.exists("nul")
False
>>> os.path.exists("prn")
False
This is in Windows 2000 (5.00.2195) sp4, using *both* Python 2.3.5 and
2.5.1, no cygwin.
Personally, I'm +1 with Mark Hammond about this:
I agree it is unfortunate that the behaviour has changed,
but these special names are broken enough on Windows that
rely on the kernel32 function and behaves like it says
seems the sanest thing to do.
Taking in consideration that *now* it behaves equally in different
windows systems, but not before, I think this issue should be closed as
"invalid" (it's not a bug).
I'll wait some days to get more behaviour responses, though.
Regards,
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msg56873 - (view) |
Author: Gabriel Genellina (ggenellina) |
Date: 2007-10-28 01:55 |
All these tests on Windows XP SP4, executing os.stat("nul")
Python 2.1 thru 2.4 raises:
OSError: [Errno 22] Invalid argument: 'nul'
Python 2.5 gives a different error:
WindowsError: [Error 87] El parámetro no es correcto: 'nul'
|
msg350122 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-21 22:27 |
New changeset df2d4a6f3d5da2839c4fc11d31511c8e028daf2c by Steve Dower in branch 'master':
bpo-37834: Normalise handling of reparse points on Windows (GH-15231)
https://github.com/python/cpython/commit/df2d4a6f3d5da2839c4fc11d31511c8e028daf2c
|
msg350124 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-21 22:34 |
Well, I was trying not to resurrect this old issue, but looks like I did it accidentally.
Hi there, old hands! We miss you :)
We also figured out a new [l]stat() implementation on Windows that handles symlinks and junctions better, and also non-file types such as NUL. So I guess I'll mark this as resolved in Python 3.8
|
msg350126 - (view) |
Author: Steve Dower (steve.dower) * |
Date: 2019-08-21 22:52 |
New changeset 9eb3d5463976068900e94b860ced7e035885835c by Steve Dower in branch '3.8':
bpo-37834: Normalise handling of reparse points on Windows (GH-15370)
https://github.com/python/cpython/commit/9eb3d5463976068900e94b860ced7e035885835c
|
|
Date |
User |
Action |
Args |
2022-04-11 14:56:27 | admin | set | github: 45652 |
2019-08-21 22:52:45 | steve.dower | set | messages:
+ msg350126 |
2019-08-21 22:34:28 | steve.dower | set | resolution: not a bug -> fixed stage: resolved messages:
+ msg350124 versions:
+ Python 3.8, Python 3.9, - Python 2.5 |
2019-08-21 22:31:04 | steve.dower | set | pull_requests:
+ pull_request15082 |
2019-08-21 22:27:36 | steve.dower | set | nosy:
+ steve.dower messages:
+ msg350122
|
2008-02-23 21:19:36 | akuchling | set | status: open -> closed resolution: not a bug |
2007-10-28 01:55:07 | ggenellina | set | nosy:
+ ggenellina messages:
+ msg56873 |
2007-10-26 17:07:12 | facundobatista | set | messages:
+ msg56795 |
2007-10-25 05:21:25 | loewis | set | messages:
+ msg56735 |
2007-10-25 04:05:41 | loewis | set | messages:
+ msg56734 |
2007-10-25 04:01:57 | loewis | set | nosy:
+ loewis messages:
+ msg56733 |
2007-10-23 20:56:48 | kdwyer | set | messages:
+ msg56692 |
2007-10-23 17:37:11 | kdwyer | set | nosy:
+ kdwyer messages:
+ msg56684 |
2007-10-23 07:09:27 | d_kagedal | set | messages:
+ msg56674 |
2007-10-22 17:13:49 | facundobatista | set | nosy:
+ facundobatista messages:
+ msg56652 |
2007-10-22 12:23:20 | d_kagedal | set | messages:
+ msg56645 title: os.path.exists(os.devnul) regression on windows -> os.path.exists(os.devnull) regression on windows |
2007-10-22 12:04:18 | d_kagedal | create | |