[3.13] gh-59000: Fix pdb breakpoint resolution for class methods when module not imported (GH-141949)

(cherry picked from commit 5e58548)

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

Author: cocolato

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 +4013,54 @@ def f(x):
             self.assertIn('42', stdout)
             self.assertIn('return x + 1', stdout)
 
+    def test_zipimport(self):
+        with os_helper.temp_dir() as temp_dir:
+            os.mkdir(os.path.join(temp_dir, 'source'))
+            zipmodule = textwrap.dedent(
+                """
+                def bar():
+                    pass
+                """
+            )
+            script = textwrap.dedent(
+                f"""
+                import sys; sys.path.insert(0, {repr(os.path.join(temp_dir, 'zipmodule.zip'))})
+                import foo
+                foo.bar()
+                """
+            )
+
+            with zipfile.ZipFile(os.path.join(temp_dir, 'zipmodule.zip'), 'w') as zf:
+                zf.writestr('foo.py', zipmodule)
+            with open(os.path.join(temp_dir, 'script.py'), 'w') as f:
+                f.write(script)
+
+            stdout, _ = self._run_pdb([os.path.join(temp_dir, 'script.py')], '\n'.join([
+                'n',
+                'n',
+                'b foo.bar',
+                'c',
+                'p f"break in {$_frame.f_code.co_name}"',
+                'q'
+            ]))
+            self.assertIn('break in bar', 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.