gh-106727: Add __module__ check for inspect.getsource(cls)

Lib/inspect.py

@@ -1078,7 +1078,8 @@ def get_lineno(self):
 
             # First, let's see if there are any method definitions
             for member in self.cls.__dict__.values():
-                if isinstance(member, types.FunctionType):
+                if (isinstance(member, types.FunctionType) and
+                    member.__module__ == self.cls.__module__):
                     for lineno, end_lineno in self.lineno_found:
                         if lineno <= member.__code__.co_firstlineno <= end_lineno:
                             return lineno

Lib/test/test_inspect.py

@@ -15,6 +15,7 @@
 import shutil
 import sys
 import types
+import tempfile
 import textwrap
 import unicodedata
 import unittest
@@ -963,6 +964,33 @@ def test_nested_class_definition_inside_function(self):
         self.assertSourceEqual(mod2.cls213, 218, 222)
         self.assertSourceEqual(mod2.cls213().func219(), 220, 221)
 
+    def test_class_with_method_from_other_module(self):
+        with tempfile.TemporaryDirectory() as tempdir:
+            with open(os.path.join(tempdir, 'inspect_actual%spy' % os.extsep),
+                      'w', encoding='utf-8') as f:
+                f.write(textwrap.dedent("""
+                    import inspect_other
+                    class A:
+                        def f(self):
+                            pass
+                    class A:
+                        def f(self):
+                            pass  # correct one
+                    A.f = inspect_other.A.f
+                    """))
+
+            with open(os.path.join(tempdir, 'inspect_other%spy' % os.extsep),
+                      'w', encoding='utf-8') as f:
+                f.write(textwrap.dedent("""
+                    class A:
+                        def f(self):
+                            pass
+                    """))
+
+            with DirsOnSysPath(tempdir):
+                import inspect_actual
+                self.assertIn("correct", inspect.getsource(inspect_actual.A))
+
     @unittest.skipIf(
         support.is_emscripten or support.is_wasi,
         "socket.accept is broken"