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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.

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

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]

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

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.

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

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?

It's a problem with debug builds on Windows.
Lowering priority. 
Also, it is likely that the new import library will correct the problem.

>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?

3.1 does not use importlib for imports.

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.
>>>

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.