gh-141781: Fix pdb line prefix binding

Lib/pdb.py

@@ -654,7 +654,7 @@ def _show_display(self):
 
     def _get_tb_and_exceptions(self, tb_or_exc):
         """
-        Given a tracecack or an exception, return a tuple of chained exceptions
+        Given a traceback or an exception, return a tuple of chained exceptions
         and current traceback to inspect.
 
         This will deal with selecting the right ``__cause__`` or ``__context__``
@@ -2429,7 +2429,9 @@ def print_stack_trace(self, count=None):
         except KeyboardInterrupt:
             pass
 
-    def print_stack_entry(self, frame_lineno, prompt_prefix=line_prefix):
+    def print_stack_entry(self, frame_lineno, prompt_prefix=None):
+        if prompt_prefix is None:
+            prompt_prefix = line_prefix
         frame, lineno = frame_lineno
         if frame is self.curframe:
             prefix = '> '

Lib/test/test_pdb.py

@@ -3580,6 +3580,20 @@ def quux():
             ('bœr', 5),
         )
 
+    def test_print_stack_entry_uses_dynamic_line_prefix(self):
+        """Test that pdb.line_prefix binding is dynamic (gh-141781)."""
+        stdout = io.StringIO()
+        p = pdb.Pdb(stdout=stdout)
+
+        # Get the current frame to use for printing
+        frame = sys._getframe()
+
+        with support.swap_attr(pdb, 'line_prefix', 'CUSTOM_PREFIX> '):
+            p.print_stack_entry((frame, frame.f_lineno))
+
+        # Check if the custom prefix appeared in the output
+        self.assertIn('CUSTOM_PREFIX> ', stdout.getvalue())
+
     def test_find_function_found_with_encoding_cookie(self):
         self._assert_find_function(
             """\

Misc/ACKS

@@ -927,6 +927,7 @@ Kristján Valur Jónsson
 Jens B. Jorgensen
 John Jorgensen
 Sijin Joseph
+Paresh Joshi
 Andreas Jung
 Tattoo Mabonzo K.
 Sarah K.

Misc/NEWS.d/next/Library/2025-11-24-06-44-45.gh-issue-141781.MsK27r.rst

@@ -0,0 +1 @@
+Fixed an issue where pdb.line_prefix assignment was ignored if assigned after the module was imported.