pdb: fix expression result output stream in _exec_in_closure()

Fixes an issue where results of expressions executed via
`_exec_in_closure()` were written to `sys.stdout` instead
of the debugger output stream.
Adds a regression test to ensure expression results are
consistently emitted via pdb.stdout.

Signed-off-by: Yongtao Huang <yongtaoh2022@gmail.com>

Author: hyongtao-code

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_pdb.py

@@ -3666,6 +3666,28 @@ def test_print_stack_entry_uses_dynamic_line_prefix(self):
         # Check if the custom prefix appeared in the output
         self.assertIn('CUSTOM_PREFIX> ', stdout.getvalue())
 
+    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.
+        """
+        pdb_out = io.StringIO()
+        sys_out = io.StringIO()
+
+        p = pdb.Pdb(nosigint=True, readrc=False, stdout=pdb_out)
+
+        with redirect_stdout(sys_out):
+            self.assertTrue(p._exec_in_closure('(lambda: 123)()', {}, {}))
+            self.assertTrue(p._exec_in_closure('sum(i for i in (1, 2, 3))', {}, {}))
+
+        pdb_lines = [line.strip() for line in pdb_out.getvalue().splitlines()]
+        sys_lines = [line.strip() for line in sys_out.getvalue().splitlines()]
+
+        self.assertIn('123', pdb_lines)
+        self.assertIn('6', pdb_lines)
+        self.assertNotIn('123', sys_lines)
+        self.assertNotIn('6', sys_lines)
+
     def test_find_function_found_with_encoding_cookie(self):
         self._assert_find_function(
             """\