gh-143874: Fix pdb expression result output stream in _exec_in_closure()

Lib/pdb.py

@@ -888,7 +888,7 @@ def _exec_in_closure(self, source, globals, locals):
         locals.update(pdb_eval["write_back"])
         eval_result = pdb_eval["result"]
         if eval_result is not None:
-            print(repr(eval_result))
+            self.message(repr(eval_result))
 
         return True
 

Lib/test/test_remote_pdb.py

@@ -1441,6 +1441,34 @@ def test_multi_line_commands(self):
             self.assertIn("Function returned: 42", stdout)
             self.assertEqual(process.returncode, 0)
 
+    def test_exec_in_closure_result_uses_pdb_stdout(self):
+        """
+        Expression results executed via _exec_in_closure() should be written
+        to the debugger output stream (pdb stdout), not to sys.stdout.
+        """
+        self._create_script()
+        process, client_file = self._connect_and_get_client_file()
+
+        with kill_on_error(process):
+            self._read_until_prompt(client_file)
+
+            self._send_command(client_file, "(lambda: 123)()")
+            messages = self._read_until_prompt(client_file)
+            result_msg = "".join(msg.get("message", "") for msg in messages)
+            self.assertIn("123", result_msg)
+
+            self._send_command(client_file, "sum(i for i in (1, 2, 3))")
+            messages = self._read_until_prompt(client_file)
+            result_msg = "".join(msg.get("message", "") for msg in messages)
+            self.assertIn("6", result_msg)
+
+            self._send_command(client_file, "c")
+            stdout, _ = process.communicate(timeout=SHORT_TIMEOUT)
+
+            self.assertNotIn("\n123\n", stdout)
+            self.assertNotIn("\n6\n", stdout)
+            self.assertEqual(process.returncode, 0)
+
 
 def _supports_remote_attaching():
     PROCESS_VM_READV_SUPPORTED = False

Misc/NEWS.d/next/Library/2026-01-15-16-04-39.gh-issue-143874.1qQgvo.rst

@@ -0,0 +1 @@
+Fixed an issue in pdb where results of expressions evaluated via the closure execution path could be written to sys.stdout instead of the debugger output stream.