I tried to investigate this issue a little bit before making a contribution so maybe I can summarize what I did and my thoughts. First Here is the test that we want to make it pass:

    # TODO: RUSTPYTHON
    @unittest.expectedFailure
    def test_stdout_flush_at_shutdown(self):
        # Issue #5319: if stdout.flush() fails at shutdown, an error should
        # be printed out.
        code = """if 1:
            import os, sys, test.support
            test.support.SuppressCrashReport().__enter__()
            sys.stdout.write('x')
            os.close(sys.stdout.fileno())"""
        rc, out, err = assert_python_failure('-c', code)
        self.assertEqual(b'', out)
        self.assertEqual(120, rc)
        self.assertRegex(err.decode('ascii', 'ignore'),
                         'Exception ignored in.*\nOSError: .*')

so basically since stdout is normally buffered (unless explicitly told to not be with -u) then when the interpreter flushes right before exit it should trigger an Error like this in Cpython:

omarabdelgawad@omarabdelgawad:~$ python
Python 3.12.3 (main, Aug 14 2025, 17:47:21) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from test.support.script_helper import assert_python_failure
>>> code = """if 1:
...             import os, sys, test.support
...             test.support.SuppressCrashReport().__enter__()
...             sys.stdout.write('x')
...             os.close(sys.stdout.fileno())"""
>>> rc,out,err = assert_python_failure('-c',code)
>>> rc
120
>>> out
b''
>>> err
b"Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='utf-8'>\nOSError: [Errno 9] Bad file descriptor\n"

However the problem is that RustPython's Interpreter exits without an error:

omarabdelgawad@omarabdelgawad:~/my_workspace/RustPython$ cargo run  --release
    Finished `release` profile [optimized] target(s) in 0.11s
     Running `target/release/rustpython`
Welcome to the magnificent Rust Python 0.4.0 interpreter 😱 🖖
RustPython 3.13.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> from test.support.script_helper import assert_python_failure
>>>>> code = """if 1:
..... 		import os, sys, test.support
..... 		test.support.SuppressCrashReport().__enter__()
..... 		sys.stdout.write('x')
..... 		os.close(sys.stdout.fileno())"""
>>>>> rc, out , err = assert_python_failure('-c',code)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/omarabdelgawad/my_workspace/projects/github_repos/RustPython/pylib/Lib/test/support/script_helper.py", line 177, in assert_python_failure
    return _assert_python(False, *args, **env_vars)
  File "/home/omarabdelgawad/my_workspace/projects/github_repos/RustPython/pylib/Lib/test/support/script_helper.py", line 151, in _assert_python
    res.fail(cmd_line)
  File "/home/omarabdelgawad/my_workspace/projects/github_repos/RustPython/pylib/Lib/test/support/script_helper.py", line 90, in fail
    err))
AssertionError: Process return code is 0
command line: ['/home/omarabdelgawad/my_workspace/projects/github_repos/RustPython/target/release/rustpython', '-X', 'faulthandler', '-I', '-c', "if 1:\n\t\timport os, sys, test.support\n\t\ttest.support.SuppressCrashReport().__enter__()\n\t\tsys.stdout.write('x')\n\t\tos.close(sys.stdout.fileno())"]

stdout:
---

---

stderr:
---

---

Now I think that the interpreter flushes the stdout and stderr before exiting but probably the problem in handling them after they are closed (Bad file descriptor). so in vm/src/vm/interpreter.rs finalize function it should catch an exception in the following line no?

    pub fn finalize(self, exc: Option<PyBaseExceptionRef>) -> u8 {
        self.enter(|vm| {
            vm.flush_std(); 

            // See if any exception leaked out:
            let exit_code = if let Some(exc) = exc {
                vm.handle_exit_exception(exc)
            } else {
                0
            };
            ... // more stuff here as well
            ...
            exit_code
        })
    }

Anyways on a side note I found that the REPL crashes after os.close(1) which is the same as os.close(sys.stdout.fileno()) while CPython doesn't crash:

omarabdelgawad@omarabdelgawad:~$ python
Python 3.12.3 (main, Aug 14 2025, 17:47:21) [GCC 13.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.close(1)
>>> print("Hello")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
OSError: [Errno 9] Bad file descriptor

while RustPython crashes

omarabdelgawad@omarabdelgawad:~/my_workspace/RustPython$ ./target/debug/rustpython
Welcome to the magnificent Rust Python 0.4.0 interpreter 😱 🖖
RustPython 3.13.0
Type "help", "copyright", "credits" or "license" for more information.
>>>>> import sys,os
>>>>> os.close(sys.stdout.fileno())
Readline error: Errno(EBADF)
omarabdelgawad@omarabdelgawad:~/my_workspace/RustPython$

In order to continue working on this issue I need some help finding where builtin functions like sys.stdout.write and os.close are defined.

Flush stdout on shutdown #5521

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