`_io` and `_pyio` inconsistenly raise `ValueError`s on closed files

[sobolevn]

While working on typeshed stubs, I've noticed that _pyio.BufferedReader.read1 does not raise ValueError after .close. While _io.BufferedReader.read1 does that.

So, I went to see both implementation and tests.

C source clearly checks for this here:

cpython/Modules/_io/bufferedio.c

Line 910 in 0689b99

CHECK_CLOSED(self, "read of closed file")

But, tests were not executed correctly. Tests were only covering C version: https://github.com/python/cpython/blame/0689b99bb8c4f6058af43a52effaa8a25609dbed/Lib/test/test_io.py#L1532-L1538

    def test_read_on_closed(self):
        # Issue #23796
        b = io.BufferedReader(io.BytesIO(b"12"))
        b.read(1)
        b.close()
        self.assertRaises(ValueError, b.peek)
        self.assertRaises(ValueError, b.read1, 1)

While universal test would look like this:

    def test_read_on_closed(self):
        # Issue #23796
        b = self.BufferedReader(self.BytesIO(b"12"))
        b.read(1)
        b.close()
        self.assertRaises(ValueError, b.peek)
        self.assertRaises(ValueError, b.read1, 1)

And now it is failing:

» ./python.exe -m test -v test_io -m test_read_on_closed
== CPython 3.12.0a1+ (heads/main:7ea10567af, Oct 29 2022, 13:15:59) [Clang 11.0.0 (clang-1100.0.33.16)]
== macOS-10.14.6-x86_64-i386-64bit little-endian
== cwd: /Users/sobolev/Desktop/cpython/build/test_python_78918æ
== CPU count: 4
== encodings: locale=UTF-8, FS=utf-8
0:00:00 load avg: 2.19 Run tests sequentially
0:00:00 load avg: 2.19 [1/1] test_io
test_read_on_closed (test.test_io.CBufferedReaderTest.test_read_on_closed) ... ok
test_read_on_closed (test.test_io.PyBufferedReaderTest.test_read_on_closed) ... FAIL
test_read_on_closed (test.test_io.CBufferedRandomTest.test_read_on_closed) ... ok
test_read_on_closed (test.test_io.PyBufferedRandomTest.test_read_on_closed) ... FAIL

======================================================================
FAIL: test_read_on_closed (test.test_io.PyBufferedReaderTest.test_read_on_closed)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_io.py", line 1537, in test_read_on_closed
    self.assertRaises(ValueError, b.peek)
AssertionError: ValueError not raised by peek

======================================================================
FAIL: test_read_on_closed (test.test_io.PyBufferedRandomTest.test_read_on_closed)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython/Lib/test/test_io.py", line 1537, in test_read_on_closed
    self.assertRaises(ValueError, b.peek)
AssertionError: ValueError not raised by peek

----------------------------------------------------------------------
Ran 4 tests in 0.010s

FAILED (failures=2)

After that, I've tested other methods and here's a list of methods that work on closed in _pyio, but raises on _io:

• readinto1
• readinto
• read1
• peek

Related https://bugs.python.org/issue23796

Is it a bug or a feature? Is it worth fixing?
This clearly looks like a bug to me.

If others confirm, I have a patch ready :)

• PR: gh-98999: Raise ValueError in _pyio on closed buffers #99009

[corona10]

@sobolevn It is worth to fix it, Please send the patch.

[sobolevn]

Done :)
Thank you!