At arraymodule.c (line 1258):

		nread = fread(item + (Py_SIZE(self) - n) * itemsize,
			      itemsize, n, fp);
		if (nread < (size_t)n) {
		  Py_SIZE(self) -= (n - nread);
			PyMem_RESIZE(item, char, Py_SIZE(self)*itemsize);
			self->ob_item = item;
			self->allocated = Py_SIZE(self);
			PyErr_SetString(PyExc_EOFError,
				         "not enough items in file");
			return NULL;
		}

When fread returns 0, ferror should be called to check if it was an EOF
or an error condition. It is not handling OSErrors, such as I/O errors,
raising always "not enough items in file".

I attached a path for raising IOErrors in fromfile. I also added a
testcase which failed before.

The test opens a file and closes the file with os.close(fd) without
telling the file object, so fromfile doesn't notice it's reading from a
file that is actually closed.

Ezio, I moved the test to a separate method. Also I couldn't find
something to close the file if I don't care about errors. I thought an
assertRises would be wrong, as I am not debugging files here, so I added a
function to call a callable I expect to throw an exception (you said you
don't like the try/close/except/pass). I don't know if it is okay to add
functions to test_support, though.

There doesn't seem to be any reason to introduce the
"expect_exception()" helper, rather than to use a with statement. Am I
mistaken?

Ok, I get it, you want f.close() to always succeed, even if the
underlying file descriptor has already been closed.
Well, I so no reason to introduce a helper anyway, the following four
lines are much more readable and explicit:

try:
    f.close()
except IOError:
    pass

I tried to apply both the patches on the trunk but the tests don't pass.
With the latest patch I get an EOFError instead of IOError in the
assertRaises.

The function I was talking about was test_support.unlink(), but that
just removes the file, it doesn't close it, so the try/except is fine
when you close it (I also see that you already added
test_support.unlink() in the new patch).
I agree with Antoine that the helper function is not necessary.

A few more comments about the latest patch:

1. the try/except that imports the os module seems unnecessary to me;
2. if there are really cases where os is not available, the test should
   be skipped with a message that says that the os module is not available
   and that the test cannot be executed (with return the test is marked as
   'passed' even if nothing is actually tested);
3. if os.close(f.fileno()) is required instead of a simpler f.close()
   please write a short comment to clarify why;
4. if there are cases where EOFError is raised and they are not tested,
   it would be nice to add another test that checks if/when EOFError is raised.

1&2) I removed the try/except around the import. I have no clue if os
might be unavailable. Maybe leave out handling that until we see that
breaking.

I added the try/except because I saw that in other tests in the same
file when importing gc.

3. Done.
4. The EOFError exceptions are tested in test_tofromfile.

I tried to apply both the patches on the trunk but the tests don't
pass. With the latest patch I get an EOFError instead of IOError in
the assertRaises.
That is the also behaviour before the patch, so the ferror(fp) does not
fire. Either the test is inappropriate or your system doesn't regard
reading a closed filehandle an error. I'm not able to investigate this
as it works fine on my os x 10.6. What system did you test it on?

Reliable ways of producing IOErrors are harder to find than I thought.
Deleting the file between to reads makes it just look truncated. Another
method I tried was crashing a process which holds the other end of a
pipe, but that's messy and complicated.

Maybe you could create a file without read permission (000) and try
to read from it.

Maybe you could create a file without read permission (000) and try
to read from it.

I just checked. If I don't have read permissions, I am not able to open
the file. When I open a file and change permissions afterwards, I can read
the complete file alright. (Checked with a 4mb file, I hope that's beyond
buffering.) So I guess permissions are only checked when you open the
file.

Another try. I have opened a file for writing, and have tried to read
from it:

>>> fp = open ('xxx', 'w')
>>> fp.read ()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IOError: [Errno 9] Bad file descriptor

Thanks Aduardo! (I could have sworn I tried that.) I changed the test to
reading from a file in 'wb' mode, which raised a EOFError before and now
raises IOErrors.

With the latest patch on Windows Vista against 2.7 I got 12 EOFError errors instead of IOError.

Sorry for the noise, forgot to rebuild the code. The tests run fine 543 tests ok, except I note that all the output is repeated 6 times, I don't understand this at all.

Will polish the patch and commit.

I've committed the new test in py3k (r83030) and 3.1 (r83033), and the full patch in 2.7 (r83031) and 2.6 (r83032). Thank you!

Regarding:

The tests run fine 543 tests ok, except I note that all the output is
repeated 6 times, I don't understand this at all.

This is normal, all array tests are run once per array type, and 6 different array types are being tested.