gh-141615: Check stdin instead of stdout for use_rawinput in pdb (#141616)

Author: gaogaotiantian

Lib/pdb.py

@@ -346,8 +346,8 @@ def __init__(self, completekey='tab', stdin=None, stdout=None, skip=None,
         bdb.Bdb.__init__(self, skip=skip, backend=backend if backend else get_default_backend())
         cmd.Cmd.__init__(self, completekey, stdin, stdout)
         sys.audit("pdb.Pdb")
-        if stdout:
-            self.use_rawinput = 0
+        if stdin:
+            self.use_rawinput = False
         self.prompt = '(Pdb) '
         self.aliases = {}
         self.displaying = {}

Lib/test/test_pdb.py

@@ -4744,6 +4744,19 @@ def test_readline_not_imported(self):
         self.assertNotIn("readline imported", stdout)
         self.assertEqual(stderr, "")
 
+    def test_alternate_stdin(self):
+        script = textwrap.dedent("""
+            import pdb
+            import io
+
+            input_data = io.StringIO("p 40 + 2\\nc\\n")
+            pdb.Pdb(stdin=input_data).set_trace()
+        """)
+        commands = ""
+        stdout, stderr = self._run_script(script, commands)
+        self.assertIn("42", stdout)
+        self.assertEqual(stderr, "")
+
 
 @support.force_colorized_test_class
 class PdbTestColorize(unittest.TestCase):

Misc/NEWS.d/next/Library/2025-11-16-06-08-46.gh-issue-141615.--6EK3.rst

@@ -0,0 +1 @@
+Check ``stdin`` instead of ``stdout`` for ``use_rawinput`` in :mod:`pdb`.