[3.13] pythongh-59000: Fix pdb breakpoint resolution for class methods when… (python#142172)

* [3.13] pythongh-59000: Fix pdb breakpoint resolution for class methods when module not imported (pythonGH-141949)
(cherry picked from commit 5e58548)

Co-authored-by: LloydZ <35182391+cocolato@users.noreply.github.com>

Author: gaogaotiantian

Lib/pdb.py

@@ -1262,7 +1262,9 @@ def lineinfo(self, identifier):
             f = self.lookupmodule(parts[0])
             if f:
                 fname = f
-            item = parts[1]
+                item = parts[1]
+            else:
+                return failed
         answer = find_function(item, self.canonic(fname))
         return answer or failed
 

Lib/test/test_pdb.py

@@ -4013,6 +4013,22 @@ def f(x):
             self.assertIn('42', stdout)
             self.assertIn('return x + 1', stdout)
 
+    def test_issue_59000(self):
+        script = """
+            def foo():
+                pass
+
+            class C:
+                def foo(self):
+                    pass
+        """
+        commands = """
+            break C.foo
+            quit
+        """
+        stdout, stderr = self.run_pdb_script(script, commands)
+        self.assertIn("The specified object 'C.foo' is not a function", stdout)
+
 
 class ChecklineTests(unittest.TestCase):
     def setUp(self):

Misc/NEWS.d/next/Library/2025-11-25-16-00-29.gh-issue-59000.YtOyJy.rst

@@ -0,0 +1 @@
+Fix :mod:`pdb` breakpoint resolution for class methods when the module defining the class is not imported.