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https://github.com/python/cpython/commit/552b2646b75d079e9b31d4e800fbb2234624ed44
commit: 552b2646b75d079e9b31d4e800fbb2234624ed44
branch: 3.12
author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com>
committer: hugovk <1324225+hugovk@users.noreply.github.com>
date: 2024-03-28T11:15:16Z
summary:

[3.12] gh-117178: Recover lazy loading of self-referential modules (GH-117179) (#117319)

Co-authored-by: Chris Markiewicz <effigies@gmail.com>

files:
A Misc/NEWS.d/next/Library/2024-03-23-14-26-18.gh-issue-117178.vTisTG.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 f1bd06469cfc61..3743e6aa912fef 100644
--- a/Lib/importlib/util.py
+++ b/Lib/importlib/util.py
@@ -178,12 +178,11 @@ 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:
- # The first thread comes here multiple times as it descends the
- # call stack. The first time, it sets is_loading and triggers
- # exec_module(), which will access module.__dict__, module.__name__,
- # and/or module.__spec__, reentering this method. These accesses
- # need to be allowed to proceed without triggering the load again.
- if loader_state['is_loading'] and attr.startswith('__') and attr.endswith('__'):
+ # 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)
loader_state['is_loading'] = True

diff --git a/Lib/test/test_importlib/test_lazy.py b/Lib/test/test_importlib/test_lazy.py
index 38ab21907b58d9..4d2cc4eb62b67c 100644
--- a/Lib/test/test_importlib/test_lazy.py
+++ b/Lib/test/test_importlib/test_lazy.py
@@ -178,6 +178,24 @@ def access_module():
# Or multiple load attempts
self.assertEqual(loader.load_count, 1)

+ def test_lazy_self_referential_modules(self):
+ # Directory modules with submodules that reference the parent can attempt to access
+ # the parent module during a load. Verify that this common pattern works with lazy loading.
+ # json is a good example in the stdlib.
+ json_modules = [name for name in sys.modules if name.startswith('json')]
+ with test_util.uncache(*json_modules):
+ # Standard lazy loading, unwrapped
+ spec = util.find_spec('json')
+ loader = util.LazyLoader(spec.loader)
+ spec.loader = loader
+ module = util.module_from_spec(spec)
+ sys.modules['json'] = module
+ loader.exec_module(module)
+
+ # Trigger load with attribute lookup, ensure expected behavior
+ test_load = module.loads('{}')
+ self.assertEqual(test_load, {})
+

if __name__ == '__main__':
unittest.main()
diff --git a/Misc/NEWS.d/next/Library/2024-03-23-14-26-18.gh-issue-117178.vTisTG.rst b/Misc/NEWS.d/next/Library/2024-03-23-14-26-18.gh-issue-117178.vTisTG.rst
new file mode 100644
index 00000000000000..f9c53ebbfc3c96
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-03-23-14-26-18.gh-issue-117178.vTisTG.rst
@@ -0,0 +1,2 @@
+Fix regression in lazy loading of self-referential modules, introduced in
+gh-114781.

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