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On windows, "import nul" always succeed #47349

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On windows, "import nul" always succeed#47349
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tjguk
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OS-windows

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@amauryfa
amauryfa
opened on Jun 13, 2008
BPO 3099
Nosy @birkenfeld, @terryjreedy, @amauryfa, @tjguk, @merwok

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 = 'https://github.com/tjguk'
closed_at = <Date 2013-07-31.15:09:34.597>
created_at = <Date 2008-06-13.01:18:47.570>
labels = ['OS-windows']
title = 'On windows, "import nul" always succeed'
updated_at = <Date 2013-07-31.15:09:34.596>
user = 'https://github.com/amauryfa'

bugs.python.org fields:

activity = <Date 2013-07-31.15:09:34.596>
actor = 'tim.golden'
assignee = 'tim.golden'
closed = True
closed_date = <Date 2013-07-31.15:09:34.597>
closer = 'tim.golden'
components = ['Windows']
creation = <Date 2008-06-13.01:18:47.570>
creator = 'amaury.forgeotdarc'
dependencies = []
files = []
hgrepos = []
issue_num = 3099
keywords = []
message_count = 12.0
messages = ['68115', '68163', '68164', '68169', '68170', '69039', '83451', '83468', '112924', '112927', '137135', '194001']
nosy_count = 7.0
nosy_names = ['georg.brandl', 'terry.reedy', 'amaury.forgeotdarc', 'ocean-city', 'tim.golden', 'eric.araujo', 'markm']
pr_nums = []
priority = 'low'
resolution = 'works for me'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue3099'
versions = ['Python 2.7']

Activity

  1. amauryfa commented on Jun 13, 2008

    @amauryfa
    amauryfa
    on Jun 13, 2008
    ContributorAuthor

    on Windows, the stat() function always returns True for some special
    device names (nul, con, com1, lpt1...), even when followed by an extension.

    Thus "import con" manages to find that "con.py" exists, and tries to
    read from it... fun.

    A solution is to use GetFileAttributes() instead.

    Note that on python2.5.2, the error message suggest that we have such a
problem, but fortunately the error is still an ImportError::
  >>> import nul
  ImportError: DLL load failed: Le module spécifié est introuvable.
  2. amauryfa
    added
    OS-windows
    on Jun 13, 2008

  3. birkenfeld commented on Jun 13, 2008

    @birkenfeld
    birkenfeld
    on Jun 13, 2008
    Member

    The title is misleading -- if what you show is correct then "import nul"
    doesn't succeed :)

  4. amauryfa commented on Jun 13, 2008

    @amauryfa
    amauryfa
    on Jun 13, 2008
    ContributorAuthor

    Sorry, I was not clear.
    With python 2.5.2, "import nul" correctly raises ImportError, even if
    the error message is slightly misleading.

    With a recent release25-maint (and all other branches), "import nul"
    does succeed, and creates an empty module.
    "import con" seems to block, it actually waits for the user to enter
    text and type ^Z. Then it prints to the console some bizarre text that
    looks like the content of a .pyc file:

    Python 2.5.3a0 (release25-maint, Jun 11 2008, 13:17:36) [MSC v.1200 32
bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import con
^Z
a=1
b=2
c=3
^Z
│≥
    c        ☺   @   s►   d  Z  d☺ Z☺ d☻ S(♥   i☻   i♥   N(☻   t☺   bt☺
  c(    (    (    s♠   con.py   <module>☺   s☻   ♠☺    [27520 refs]
>>> dir(con)
['__builtins__', '__doc__', '__file__', '__name__', 'b', 'c']
[27533 refs]

  5. amauryfa commented on Jun 13, 2008

    @amauryfa
    amauryfa
    on Jun 13, 2008
    ContributorAuthor

    I was wrong. It seems that an installed python works correctly, but a
    python running from its build directory has the problem.

  6. amauryfa commented on Jun 13, 2008

    @amauryfa
    amauryfa
    on Jun 13, 2008
    ContributorAuthor

    OK, I think I got is now. The difference is between debug and release
    builds.

    Explanation:

    • in release build, "import nul" calls stat("nul.pyd") which succeeds.
      It then tries LoadLibrary("nul.pyd"), which fails with a DLL error.
    • in debug builds, "import nul" first tries stat("nul_d.pyd") which
      fails. It then tries stat("nul.py"), which succeeds to return an empty file!

    Whaaaa.

  7. ocean-city commented on Jul 1, 2008

    @ocean-city
    ocean-citymannequin
    on Jul 1, 2008
    Mannequin

    GetFileAttributes() succeeds for "nul", but GetFileAttributesEx() fails.
    Maybe is it good idea to use GetFileAttributesEx()?

    # test code

    import ctypes
import ctypes.wintypes as type

dll = ctypes.windll.kernel32

    print dll.GetFileAttributesA("nul") # 32

    class WIN32_FILE_ATTRIBUTE_DATA(ctypes.Structure):
	_fields_ = [("dwFileAttributes", type.DWORD),
	            ("ftCreationTime", type.FILETIME),
	            ("ftLastAccessTime", type.FILETIME),
	            ("ftLastWriteTime", type.FILETIME),
	            ("nFileSizeHigh", type.DWORD),
	            ("nFileSizeLow", type.DWORD)]

GetFileExInfoStandard = 0

wfad = WIN32_FILE_ATTRIBUTE_DATA()

    print dll.GetFileAttributesExA("nul", GetFileExInfoStandard,
    ctypes.byref(wfad)) # 0

  8. devdanzin
    assigned
    brettcannon
    on Feb 11, 2009

  9. brettcannon commented on Mar 11, 2009

    @brettcannon
    brettcannon
    on Mar 11, 2009
    Member

    Since I don't have access to Windows I am unassigning. Amaury, if this
    is still a problem should we go ahead and switch to
    GetFileAttributesEx()? Or just realize this is a problem for people
    developing Python?

  10. brettcannon
    removed their assignment
    on Mar 11, 2009

  11. amauryfa commented on Mar 11, 2009

    @amauryfa
    amauryfa
    on Mar 11, 2009
    ContributorAuthor

    It's a problem with debug builds on Windows.
    Lowering priority.

    Also, it is likely that the new import library will correct the problem.

  12. terryjreedy commented on Aug 4, 2010

    @terryjreedy
    terryjreedy
    on Aug 4, 2010
    Member

    it is likely that the new import library will correct the problem.

    Did it?

    With standard 3.1.2,
>>> import nul
...
ImportError: DLL load failed: The specified module could not be found.
>>> import con
...
ImportError: No module named con

    So is there any problem with 2.7, or should we close this?

  13. merwok commented on Aug 4, 2010

    @merwok
    merwok
    on Aug 4, 2010
    Member

    3.1 does not use importlib for imports.

  14. tjguk
    self-assigned this
    on Aug 13, 2010

  15. markm commented on May 28, 2011

    @markm
    markmmannequin
    on May 28, 2011
    Mannequin

    I am not sure that I fully understand the issue - but it seems that trunk still has this issue.
    As stated by Amaury - this is on DEBUG builds only.

    c:\>pcbuild\python_d.exe
Python 3.3a0 (default, May 28 2011, 20:22:11) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import nul
[60967 refs]
>>> import con
^Z
[60986 refs]

c:\>PCbuild\python.exe
Python 3.3a0 (default, May 28 2011, 20:25:13) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import nul
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: DLL load failed: The parameter is incorrect.
>>> import con
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: DLL load failed: The specified module could not be found.
>>>

  16. tjguk commented on Jul 31, 2013

    @tjguk
    tjguk
    on Jul 31, 2013
    Member

    This one seems to have been fixed by the importlib rebuild. I haven't bothered to trace the code path, but certainly "import nul" returns the expected "ImportError: No module named 'nul'" in both Debug & Release builds.

  17. tjguk
    closed this as completedon Jul 31, 2013
  18. ezio-melotti
    transferred this issue fromon Apr 10, 2022
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