Fix IOBase.isatty() to raise ValueError on closed files (#7233)

* Fix IOBase.isatty() to raise ValueError on closed files

* Add snippet test for IOBase.isatty() closed check

crates/vm/src/stdlib/io.rs

@@ -477,8 +477,9 @@ mod _io {
         }
 
         #[pymethod]
-        fn isatty(_self: PyObjectRef) -> bool {
-            false
+        fn isatty(instance: PyObjectRef, vm: &VirtualMachine) -> PyResult<bool> {
+            check_closed(&instance, vm)?;
+            Ok(false)
         }
 
         #[pygetset]

extra_tests/snippets/stdlib_io.py

@@ -1,5 +1,5 @@
 import os
-from io import BufferedReader, BytesIO, FileIO, StringIO
+from io import BufferedReader, BytesIO, FileIO, RawIOBase, StringIO
 
 from testutils import assert_raises
 
@@ -40,3 +40,20 @@ with FileIO("README.md") as fio:
     assert len(nres) == 1
     nres = fio.read(2)
     assert len(nres) == 2
+
+# Test that IOBase.isatty() raises ValueError when called on a closed file.
+# Minimal subclass that inherits IOBase.isatty() without overriding it.
+class MinimalRaw(RawIOBase):
+    def readinto(self, b):
+        return 0
+
+
+f = MinimalRaw()
+assert not f.closed
+assert not f.isatty()  # open file: should return False
+
+f.close()
+assert f.closed
+
+with assert_raises(ValueError):
+    f.isatty()