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[3.15] gh-148587: Make sys.lazy_modules match PEP and keep internal lazy submodules tra… #150014

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5fa41ef
Make sys.lazy_modules match PEP and keep internal lazy submodules tra…
DinoV May 18, 2026
98cacb1
📜🤖 Added by blurb_it.
blurb-it[bot] May 18, 2026
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7 changes: 7 additions & 0 deletions Include/internal/pycore_interp_structs.h
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Original file line number Diff line number Diff line change
Expand Up @@ -349,7 +349,14 @@ struct _import_state {
int lazy_imports_mode;
PyObject *lazy_imports_filter;
PyObject *lazy_importing_modules;
// The set stored in sys.lazy_modules if values that have been
// lazily imported. This value is only for debugging/introspection
// purposes and is not used at runtime.
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@Yhg1s Yhg1s May 18, 2026

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Suggested change
// purposes and is not used at runtime.
// purposes and is not used by the runtime.

PyObject *lazy_modules;
// Submodules that have been imported lazily from modules which have
// been imported lazily. When the module is imported we need to add
// a LazyImportObject which refers to the submodule on the module.
Comment on lines +356 to +358
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@Yhg1s Yhg1s May 18, 2026

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Suggested change
// Submodules that have been imported lazily from modules which have
// been imported lazily. When the module is imported we need to add
// a LazyImportObject which refers to the submodule on the module.
// A dict mapping package names to a set of submodule names that
// have been imported lazily from packages which have been imported
// lazily. When the package is reified we need to add a
// LazyImportObject which refers to the submodule on the module.

PyObject *lazy_pending_submodules;
#ifdef Py_GIL_DISABLED
PyMutex lazy_mutex;
#endif
Expand Down
27 changes: 10 additions & 17 deletions Lib/test/test_lazy_import/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -37,8 +37,7 @@ def test_basic_unused(self):
"""Lazy imported module should not be loaded if never accessed."""
import test.test_lazy_import.data.basic_unused
self.assertNotIn("test.test_lazy_import.data.basic2", sys.modules)
self.assertIn("test.test_lazy_import.data", sys.lazy_modules)
self.assertEqual(sys.lazy_modules["test.test_lazy_import.data"], {"basic2"})
self.assertIn("test.test_lazy_import.data.basic2", sys.lazy_modules)

def test_sys_lazy_modules(self):
try:
Expand All @@ -48,7 +47,7 @@ def test_sys_lazy_modules(self):

self.assertFalse("test.test_lazy_import.data.basic2" in sys.modules)
self.assertIn("test.test_lazy_import.data", sys.lazy_modules)
self.assertEqual(sys.lazy_modules["test.test_lazy_import.data"], {"basic2"})
self.assertIn("test.test_lazy_import.data.basic2", sys.lazy_modules)
test.test_lazy_import.data.basic_from_unused.basic2
self.assertNotIn("test.test_import.data", sys.lazy_modules)

Expand Down Expand Up @@ -569,8 +568,8 @@ def my_filter(name):
self.assertIs(sys.get_lazy_imports_filter(), my_filter)

def test_lazy_modules_attribute_is_dict(self):
"""sys.lazy_modules should be a dict per PEP 810."""
self.assertIsInstance(sys.lazy_modules, dict)
"""sys.lazy_modules should be a set per PEP 810."""
self.assertIsInstance(sys.lazy_modules, set)

@support.requires_subprocess()
def test_lazy_modules_tracks_lazy_imports(self):
Expand All @@ -579,8 +578,7 @@ def test_lazy_modules_tracks_lazy_imports(self):
import sys
initial_count = len(sys.lazy_modules)
import test.test_lazy_import.data.basic_unused
assert "test.test_lazy_import.data" in sys.lazy_modules
assert sys.lazy_modules["test.test_lazy_import.data"] == {"basic2"}
assert "test.test_lazy_import.data.basic2" in sys.lazy_modules
assert len(sys.lazy_modules) > initial_count
print("OK")
""")
Expand Down Expand Up @@ -1029,15 +1027,14 @@ def test_module_added_to_lazy_modules_on_lazy_import(self):
lazy import test.test_lazy_import.data.basic2

# Should be in lazy_modules after lazy import
assert "test.test_lazy_import.data" in sys.lazy_modules
assert sys.lazy_modules["test.test_lazy_import.data"] == {"basic2"}
assert "test.test_lazy_import.data.basic2" in sys.lazy_modules
assert len(sys.lazy_modules) > initial_count

# Trigger reification
_ = test.test_lazy_import.data.basic2.x

# Module should still be tracked (for diagnostics per PEP 810)
assert "test.test_lazy_import.data" not in sys.lazy_modules
assert "test.test_lazy_import.data.basic2" not in sys.lazy_modules
print("OK")
""")
result = subprocess.run(
Expand All @@ -1050,8 +1047,8 @@ def test_module_added_to_lazy_modules_on_lazy_import(self):

def test_lazy_modules_is_per_interpreter(self):
"""Each interpreter should have independent sys.lazy_modules."""
# Basic test that sys.lazy_modules exists and is a dict
self.assertIsInstance(sys.lazy_modules, dict)
# Basic test that sys.lazy_modules exists and is a set
self.assertIsInstance(sys.lazy_modules, set)

def test_lazy_module_without_children_is_tracked(self):
code = textwrap.dedent("""
Expand All @@ -1060,10 +1057,6 @@ def test_lazy_module_without_children_is_tracked(self):
assert "json" in sys.lazy_modules, (
f"expected 'json' in sys.lazy_modules, got {set(sys.lazy_modules)}"
)
assert sys.lazy_modules["json"] == set(), (
f"expected empty set for sys.lazy_modules['json'], "
f"got {sys.lazy_modules['json']!r}"
)
print("OK")
""")
assert_python_ok("-c", code)
Expand Down Expand Up @@ -1932,7 +1925,7 @@ def create_lazy_imports(idx):
t.join()

assert not errors, f"Errors: {errors}"
assert isinstance(sys.lazy_modules, dict), "sys.lazy_modules is not a dict"
assert isinstance(sys.lazy_modules, set), "sys.lazy_modules is not a dict"
print("OK")
""")

Expand Down
3 changes: 3 additions & 0 deletions Lib/test/test_lazy_import/__main__.py
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
import unittest

unittest.main('test.test_lazy_import')
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2026-05-18-18-36-28.gh-issue-148587.-RD3z5.rst
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@@ -0,0 +1 @@
``sys.lazy_modules`` is now a set instead of a dict as initially spelled out in PEP 810.
54 changes: 40 additions & 14 deletions Python/import.c
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Expand Up @@ -94,6 +94,8 @@ static struct _inittab *inittab_copy = NULL;
(interp)->imports.modules_by_index
#define LAZY_MODULES(interp) \
(interp)->imports.lazy_modules
#define LAZY_PENDING_SUBMODULES(interp) \
(interp)->imports.lazy_pending_submodules
#define IMPORTLIB(interp) \
(interp)->imports.importlib
#define OVERRIDE_MULTI_INTERP_EXTENSIONS_CHECK(interp) \
Expand Down Expand Up @@ -271,15 +273,19 @@ import_get_module(PyThreadState *tstate, PyObject *name)
PyObject *
_PyImport_InitLazyModules(PyInterpreterState *interp)
{
assert(LAZY_MODULES(interp) == NULL);
LAZY_MODULES(interp) = PyDict_New();
assert(LAZY_MODULES(interp) == NULL &&
LAZY_PENDING_SUBMODULES(interp) == NULL);

LAZY_PENDING_SUBMODULES(interp) = PyDict_New();
LAZY_MODULES(interp) = PySet_New(0);
return LAZY_MODULES(interp);
}

void
_PyImport_ClearLazyModules(PyInterpreterState *interp)
{
Py_CLEAR(LAZY_MODULES(interp));
Py_CLEAR(LAZY_PENDING_SUBMODULES(interp));
}

static int
Expand Down Expand Up @@ -4339,7 +4345,7 @@ get_mod_dict(PyObject *module)
// ensure we have the set for the parent module name in sys.lazy_modules.
// Returns a new reference.
static PyObject *
ensure_lazy_submodules(PyDictObject *lazy_modules, PyObject *parent)
ensure_lazy_pending_submodules(PyDictObject *lazy_modules, PyObject *parent)
{
PyObject *lazy_submodules;
Py_BEGIN_CRITICAL_SECTION(lazy_modules);
Expand All @@ -4358,6 +4364,9 @@ ensure_lazy_submodules(PyDictObject *lazy_modules, PyObject *parent)
return lazy_submodules;
}

// Ensures that we have a LazyImportObject on the parent module for
// all children modules which have been lazily imported. If the parent
// module overrides the child attribute then the value is not replaced.
static int
register_lazy_on_parent(PyThreadState *tstate, PyObject *name,
PyObject *builtins)
Expand All @@ -4369,16 +4378,16 @@ register_lazy_on_parent(PyThreadState *tstate, PyObject *name,
PyObject *parent_dict = NULL;

PyInterpreterState *interp = tstate->interp;
PyObject *lazy_modules = LAZY_MODULES(interp);
assert(lazy_modules != NULL);
PyObject *lazy_pending_submodules = LAZY_PENDING_SUBMODULES(interp);
assert(lazy_pending_submodules != NULL);

Py_INCREF(name);
while (true) {
Py_ssize_t dot = PyUnicode_FindChar(name, '.', 0,
PyUnicode_GET_LENGTH(name), -1);
if (dot < 0) {
PyObject *lazy_submodules = ensure_lazy_submodules(
(PyDictObject *)lazy_modules, name);
PyObject *lazy_submodules = ensure_lazy_pending_submodules(
(PyDictObject *)lazy_pending_submodules, name);
if (lazy_submodules == NULL) {
goto done;
}
Expand All @@ -4400,8 +4409,8 @@ register_lazy_on_parent(PyThreadState *tstate, PyObject *name,
}

// Record the child as being lazily imported from the parent.
PyObject *lazy_submodules = ensure_lazy_submodules(
(PyDictObject *)lazy_modules, parent);
PyObject *lazy_submodules = ensure_lazy_pending_submodules(
(PyDictObject *)lazy_pending_submodules, parent);
if (lazy_submodules == NULL) {
goto done;
}
Expand Down Expand Up @@ -4464,6 +4473,14 @@ register_from_lazy_on_parent(PyThreadState *tstate, PyObject *abs_name,
if (fromname == NULL) {
return -1;
}

// Add the module name to sys.lazy_modules set (PEP 810).
PyObject *lazy_modules = LAZY_MODULES(tstate->interp);
if (PySet_Add(lazy_modules, fromname) < 0) {
Py_DECREF(fromname);
return -1;
}

int res = register_lazy_on_parent(tstate, fromname, builtins);
Py_DECREF(fromname);
return res;
Expand Down Expand Up @@ -4555,6 +4572,13 @@ _PyImport_LazyImportModuleLevelObject(PyThreadState *tstate,
Py_DECREF(abs_name);
return NULL;
}

// Add the module name to sys.lazy_modules set (PEP 810).
PyObject *lazy_modules = LAZY_MODULES(tstate->interp);
if (PySet_Add(lazy_modules, abs_name) < 0) {
goto error;
}

if (fromlist && PyUnicode_Check(fromlist)) {
if (register_from_lazy_on_parent(tstate, abs_name, fromlist,
builtins) < 0) {
Expand Down Expand Up @@ -4791,6 +4815,7 @@ _PyImport_ClearCore(PyInterpreterState *interp)
Py_CLEAR(IMPORTLIB(interp));
Py_CLEAR(IMPORT_FUNC(interp));
Py_CLEAR(LAZY_IMPORT_FUNC(interp));
Py_CLEAR(interp->imports.lazy_pending_submodules);
Py_CLEAR(interp->imports.lazy_modules);
Py_CLEAR(interp->imports.lazy_importing_modules);
Py_CLEAR(interp->imports.lazy_imports_filter);
Expand Down Expand Up @@ -5636,11 +5661,13 @@ _imp__set_lazy_attributes_impl(PyObject *module, PyObject *modobj,
PyThreadState *tstate = _PyThreadState_GET();
PyObject *module_dict = NULL;
PyObject *ret = NULL;
PyObject *lazy_modules = LAZY_MODULES(tstate->interp);
assert(lazy_modules != NULL);
PyObject *lazy_pending_modules = LAZY_PENDING_SUBMODULES(tstate->interp);
assert(lazy_pending_modules != NULL);

PyObject *lazy_submodules;
if (PyDict_GetItemRef(lazy_modules, name, &lazy_submodules) < 0) {
if (PySet_Discard(LAZY_MODULES(tstate->interp), name) < 0) {
return NULL;
} else if (PyDict_GetItemRef(lazy_pending_modules, name, &lazy_submodules) < 0) {
return NULL;
}
else if (lazy_submodules == NULL) {
Expand All @@ -5659,8 +5686,7 @@ _imp__set_lazy_attributes_impl(PyObject *module, PyObject *modobj,
Py_END_CRITICAL_SECTION();
Py_DECREF(lazy_submodules);

// once a module is imported it is removed from sys.lazy_modules
if (PyDict_DelItem(lazy_modules, name) < 0) {
if (PyDict_DelItem(lazy_pending_modules, name) < 0) {
goto error;
}

Expand Down
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