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https://github.com/python/cpython/commit/19a22020676a599e1c92a24f841196645ddd9895
commit: 19a22020676a599e1c92a24f841196645ddd9895
branch: main
author: Chris Markiewicz <effigies@gmail.com>
committer: FFY00 <filipe.lains@gmail.com>
date: 2024-04-09T04:08:48+01:00
summary:

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

files:
A Misc/NEWS.d/next/Library/2024-03-23-12-28-05.gh-issue-117182.a0KANW.rst
M Lib/importlib/util.py
M Lib/test/test_importlib/test_lazy.py

diff --git a/Lib/importlib/util.py b/Lib/importlib/util.py
index f1bb4b1fb41576..c94a148e4c50e0 100644
--- a/Lib/importlib/util.py
+++ b/Lib/importlib/util.py
@@ -178,15 +178,17 @@ def __getattribute__(self, attr):
# Only the first thread to get the lock should trigger the load
# and reset the module's class. The rest can now getattr().
if object.__getattribute__(self, '__class__') is _LazyModule:
+ __class__ = loader_state['__class__']
+
# Reentrant calls from the same thread must be allowed to proceed without
# triggering the load again.
# exec_module() and self-referential imports are the primary ways this can
# happen, but in any case we must return something to avoid deadlock.
if loader_state['is_loading']:
- return object.__getattribute__(self, attr)
+ return __class__.__getattribute__(self, attr)
loader_state['is_loading'] = True

- __dict__ = object.__getattribute__(self, '__dict__')
+ __dict__ = __class__.__getattribute__(self, '__dict__')

# All module metadata must be gathered from __spec__ in order to avoid
# using mutated values.
@@ -216,8 +218,10 @@ def __getattribute__(self, attr):
# Update after loading since that's what would happen in an eager
# loading situation.
__dict__.update(attrs_updated)
- # Finally, stop triggering this method.
- self.__class__ = types.ModuleType
+ # Finally, stop triggering this method, if the module did not
+ # already update its own __class__.
+ if isinstance(self, _LazyModule):
+ object.__setattr__(self, '__class__', __class__)

return getattr(self, attr)

diff --git a/Lib/test/test_importlib/test_lazy.py b/Lib/test/test_importlib/test_lazy.py
index 4d2cc4eb62b67c..5c6e0303528906 100644
--- a/Lib/test/test_importlib/test_lazy.py
+++ b/Lib/test/test_importlib/test_lazy.py
@@ -196,6 +196,34 @@ def test_lazy_self_referential_modules(self):
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()
diff --git a/Misc/NEWS.d/next/Library/2024-03-23-12-28-05.gh-issue-117182.a0KANW.rst b/Misc/NEWS.d/next/Library/2024-03-23-12-28-05.gh-issue-117182.a0KANW.rst
new file mode 100644
index 00000000000000..6b3b841d9d5d7b
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-03-23-12-28-05.gh-issue-117182.a0KANW.rst
@@ -0,0 +1,2 @@
+Lazy-loading of modules that modify their own ``__class__`` no longer
+reverts the ``__class__`` to :class:`types.ModuleType`.

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