gh-59000: Fix pdb breakpoint resolution for class methods when module not imported

Lib/pdb.py

@@ -1487,7 +1487,9 @@ 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

@@ -4587,6 +4587,35 @@ def bar():
             ]))
             self.assertIn('break in bar', stdout)
 
+    def test_issue_59000(self):
+        script = """
+            def foo():
+                test_str = "break foo"
+
+            class C:
+                def foo(self):
+                    test_str = "break C.foo"
+
+            foo()
+            C().foo()
+        """
+        commands = """
+            break foo
+            break C.foo
+            continue
+            break C.foo
+            continue
+            quit
+        """
+        stdout, stderr = self.run_pdb_script(script, commands)
+        res_lines = [x.strip() for x in stdout.splitlines()]
+        # can't set breakpoint before class C is defined, and gives an error
+        self.assertIn("The specified object 'C.foo' is not a function", res_lines[3])
+        # can set correctly after the class C is defined
+        self.assertRegex(res_lines[6], r"Breakpoint 2 at .*main\.py:7")
+        self.assertIn('test_str = "break C.foo"', res_lines[8])
+
+
 
 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.