gh-132962: _pyrepl: Prevent crash on Windows when stdout is redirected

Lib/_pyrepl/main.py

@@ -11,6 +11,8 @@
         raise RuntimeError("Windows 10 TH2 or later required")
     if not os.isatty(sys.stdin.fileno()):
         raise OSError(errno.ENOTTY, "tty required", "stdin")
+    if sys.platform == "win32" and not os.isatty(sys.stdout.fileno()):
+        raise OSError(errno.ENOTTY, "tty required", "stdout")
     from .simple_interact import check
     if err := check():
         raise RuntimeError(err)

Lib/test/test_pyrepl/test_windows_console.py

@@ -5,6 +5,9 @@
     raise unittest.SkipTest("test only relevant on win32")
 
 
+import subprocess
+from tempfile import TemporaryDirectory
+import os
 import itertools
 from functools import partial
 from test.support import force_not_colorized_test_class
@@ -577,5 +580,34 @@ def test_up_vt(self):
         self.assertEqual(self.mock.call_count, 3)
 
 
+class WindowsCommandLineTests(unittest.TestCase):
+    def test_for_crash_traceback_with_redirected_stdout(self):
+        """python.bat -i -c "print('hlwd')" > file.txt"""
+        script_command = "print('script has run')"
+        with TemporaryDirectory() as tmp_dir:
+            stdout_path = os.path.join(tmp_dir, "WinCMDLineTests.txt")
+            with open(stdout_path, "w") as stdout_file, \
+                subprocess.Popen(
+                    [sys.executable, '-i', '-c', script_command],
+                    stdin=None,
+                    stdout=stdout_file,
+                    stderr=subprocess.PIPE,
+                    text=True, errors='replace'
+                ) as process:
+                stderr_output = ""
+                try:
+                    process.wait(timeout=3)
+                except subprocess.TimeoutExpired:
+                    process.kill()
+                    _, stderr_output = process.communicate()
+                has_crash_traceback = (
+                    "OSError" in stderr_output and
+                    len(stderr_output) > 1200
+                )
+                if has_crash_traceback:
+                    self.fail("Detected endless OSError traceback."
+                          f"\n--- stderr ---\n{stderr_output[:1200]}")
+
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Windows/2025-06-13-19-18-00.gh-issue-132962.qOquLB.rst

@@ -0,0 +1,3 @@
+The interactive interpreter (-i) on Windows no longer crashes when standard
+output is redirected. It now correctly falls back to the basic REPL in this
+situation.