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Import a lazy submodule that a package attribute shadows
_Py_module_getattro_impl consults lazy_pending_submodules only once ordinary lookup has missed, so a `sub` bound by pkg/__init__.py answers the read that was meant to trigger a pending `import pkg.sub`, and the submodule is never imported. An eager `import pkg.sub` replaces that attribute with the submodule, so the two modes disagree. Bind the submodule on the package instead, at the two points where the eager import would have: when the package finishes loading, and at registration when it is already loaded. _imp._set_lazy_attributes() now does what its name, and the comment on lazy_pending_submodules, already describe. That needs to tell `import a.b`, whose last component must be a submodule, from `from a import b` and `import a.b as x`, whose last component may be an ordinary attribute. lazy_pending_submodules now records which of the two a pending name came from, and IMPORT_FROM retracts the claim for the `as` form before anything is resolved. The repro in pythongh-151208 was fixed by pythongh-155194; this covers the shapes that survived it -- a sibling or parent import rebinding the name, and a lazy submodule registered after its package is loaded.
1 parent fcf0411 commit 00da645

9 files changed

Lines changed: 196 additions & 111 deletions

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‎Include/internal/pycore_import.h‎

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@@ -49,6 +49,8 @@ extern _PyLazySubmoduleImportResult _PyImport_TryLoadLazySubmodule(
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extern PyObject * _PyImport_LazyImportModuleLevelObject(
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PyThreadState *tstate, PyObject *name, PyObject *builtins,
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PyObject *globals, PyObject *locals, PyObject *fromlist, int level);
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extern int _PyImport_UnmarkPendingSubmodule(
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PyThreadState *tstate, PyObject *parent, PyObject *child);
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#ifdef HAVE_DLOPEN

‎Lib/test/test_lazy_import/__init__.py‎

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@@ -2,6 +2,7 @@
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import io
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import dis
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import importlib
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import subprocess
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import sys
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import textwrap
@@ -2209,27 +2210,27 @@ def test_import_after_variable_wins(self):
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]
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self.assertIs(module_same_name_var_order2.bar, bar_mod)
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def test_import_of_parent_keeps_pending_submodule(self):
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"""`import pkg` should not discard a pending `import pkg.sub`."""
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# gh-151208: both statements bind `pkg`, and the submodule is
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# shadowed by an attribute of the package, so dropping the pending
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# import leaves that attribute in place instead of the submodule.
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from test.test_lazy_import.data import (
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import_parent_after_submodule as mod)
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# gh-151208: `import pkg.sub` imports the submodule even when the package
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# binds its own `sub`, as the eager import does.
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def check_shadowed_submodule(self, driver):
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mod = importlib.import_module(f"test.test_lazy_import.data.{driver}")
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pkg = mod.test.test_lazy_import.data.submodule_name_shadowed
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sub = pkg.sub
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self.assertIsInstance(sub, types.ModuleType)
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self.assertIs(sub, sys.modules[
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self.assertIsInstance(pkg.sub, types.ModuleType)
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self.assertIs(pkg.sub, sys.modules[
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"test.test_lazy_import.data.submodule_name_shadowed.sub"
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])
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def test_import_of_parent_keeps_pending_submodule_in_all_mode(self):
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"""Plain imports made lazy by 'all' mode behave the same way."""
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sys.set_lazy_imports("all")
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from test.test_lazy_import.data import (
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plain_import_parent_after_submodule as mod)
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pkg = mod.test.test_lazy_import.data.submodule_name_shadowed
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self.assertIsInstance(pkg.sub, types.ModuleType)
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def test_shadowed_submodule_then_parent_import(self):
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"""A later `import pkg` should not lose a pending `import pkg.sub`."""
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self.check_shadowed_submodule("import_parent_after_submodule")
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def test_shadowed_submodule_then_sibling_import(self):
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"""A later `import pkg.other` should not lose it either."""
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self.check_shadowed_submodule("import_sibling_after_submodule")
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def test_shadowed_submodule_of_loaded_parent(self):
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"""A pending submodule binds on a package that is already loaded."""
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self.check_shadowed_submodule("lazy_submodule_of_loaded_parent")
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class DeletedModuleReimportTests(unittest.TestCase):

‎Lib/test/test_lazy_import/data/import_sibling_after_submodule.py‎

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lazy import test.test_lazy_import.data.submodule_name_shadowed.sub
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lazy import test.test_lazy_import.data.submodule_name_shadowed.other

‎Lib/test/test_lazy_import/data/lazy_submodule_of_loaded_parent.py‎

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import test.test_lazy_import.data.submodule_name_shadowed
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lazy import test.test_lazy_import.data.submodule_name_shadowed.sub

‎Lib/test/test_lazy_import/data/plain_import_parent_after_submodule.py‎

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This file was deleted.

‎Lib/test/test_lazy_import/data/submodule_name_shadowed/other.py‎

Whitespace-only changes.

‎Misc/NEWS.d/next/Core_and_Builtins/2026-09-18-02-49-14.gh-issue-151208.Qv7mKd.rst‎

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@@ -1,4 +1,4 @@
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Fix lazy imports dropping a pending submodule import when the package is
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imported again under its own name. ``import pkg.sub`` followed by
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``import pkg`` now still imports ``pkg.sub``, so an attribute of ``pkg``
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that shares the submodule's name no longer keeps it from being imported.
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Fix a lazy ``import pkg.sub`` never importing the submodule when
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``pkg/__init__.py`` binds its own attribute of that name. The attribute
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answered the read that was meant to trigger the import, where an eager
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``import pkg.sub`` replaces it with the submodule.

‎Python/ceval.c‎

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@@ -3360,6 +3360,10 @@ _PyEval_LazyImportFrom(PyThreadState *tstate, _PyInterpreterFrame *frame, PyObje
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if (from == NULL) {
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return NULL;
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}
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if (_PyImport_UnmarkPendingSubmodule(tstate, from, name) < 0) {
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Py_DECREF(from);
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return NULL;
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}
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ret = _PyLazyImport_New(frame, d->lz_builtins, from, name);
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Py_DECREF(from);
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return ret;
@@ -3374,6 +3378,16 @@ _PyEval_LazyImportFrom(PyThreadState *tstate, _PyInterpreterFrame *frame, PyObje
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if (from == NULL) {
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return NULL;
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}
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// Only the last component of the dotted name is in doubt; the
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// ones above it must be packages for it to be reached at all.
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int last = PyUnicode_GET_LENGTH(d->lz_from)
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== dot + 1 + PyUnicode_GET_LENGTH(name);
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if (last &&
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_PyImport_UnmarkPendingSubmodule(tstate, from, name) < 0)
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{
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Py_DECREF(from);
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return NULL;
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}
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ret = _PyLazyImport_New(frame, d->lz_builtins, from, name);
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Py_DECREF(from);
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return ret;

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