gh-117182: Allow lazily loaded modules to modify their own __class__

1 files changed, 28 insertions, 0 deletions

diff --git a/Lib/test/test_importlib/test_lazy.py b/Lib/test/test_importlib/test_lazy.py
index 4d2cc4e..5c6e030 100644
--- a/Lib/test/test_importlib/test_lazy.py
+++ b/Lib/test/test_importlib/test_lazy.py
@@ -196,6 +196,34 @@ class LazyLoaderTests(unittest.TestCase):
             test_load = module.loads('{}')
             self.assertEqual(test_load, {})
 
+    def test_lazy_module_type_override(self):
+        # Verify that lazy loading works with a module that modifies
+        # its __class__ to be a custom type.
+
+        # Example module from PEP 726
+        module = self.new_module(source_code="""\
+import sys
+from types import ModuleType
+
+CONSTANT = 3.14
+
+class ImmutableModule(ModuleType):
+    def __setattr__(self, name, value):
+        raise AttributeError('Read-only attribute!')
+
+    def __delattr__(self, name):
+        raise AttributeError('Read-only attribute!')
+
+sys.modules[__name__].__class__ = ImmutableModule
+""")
+        sys.modules[TestingImporter.module_name] = module
+        self.assertIsInstance(module, util._LazyModule)
+        self.assertEqual(module.CONSTANT, 3.14)
+        with self.assertRaises(AttributeError):
+            module.CONSTANT = 2.71
+        with self.assertRaises(AttributeError):
+            del module.CONSTANT
+
 
 if __name__ == '__main__':
     unittest.main()