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GeezerVison is showing github.com — gh-117182: Allow lazily loaded modules to modify their own __class__ by effigies · Pull Request #117185 · python/cpython

gh-117182: Allow lazily loaded modules to modify their own __class__ #117185

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Merged
FFY00 merged 3 commits into python:main from effigies:fix-issue-117182
Apr 9, 2024

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gh-117182: Allow lazily loaded modules to modify their own __class__ #117185

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933c646
gh-117182: Test interaction between lazy modules and self-modifying m…
effigies Mar 23, 2024
a5e9670
gh-117182: Allow modules to modify their own __class__ when lazily lo…
effigies Mar 23, 2024
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effigies Mar 23, 2024
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12 changes: 8 additions & 4 deletions 12 Lib/importlib/util.py
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down Expand Up @@ -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)

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28 changes: 28 additions & 0 deletions 28 Lib/test/test_importlib/test_lazy.py
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Expand Up @@ -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()
2 changes: 2 additions & 0 deletions 2 Misc/NEWS.d/next/Library/2024-03-23-12-28-05.gh-issue-117182.a0KANW.rst
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@@ -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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