python · encukou · Nov 26, 2025 · Nov 16, 2025 · Nov 16, 2025 · Nov 23, 2025
diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
@@ -241,21 +241,7 @@ def test_repeated_init_and_inittab(self):
 
     def test_create_module_from_initfunc(self):
         out, err = self.run_embedded_interpreter("test_create_module_from_initfunc")
-        if support.Py_GIL_DISABLED:
-            # the test imports a singlephase init extension, so it emits a warning
-            # under the free-threaded build
-            expected_runtime_warning = (
-                "RuntimeWarning: The global interpreter lock (GIL)"
-                " has been enabled to load module 'embedded_ext'"
-            )
-            filtered_err_lines = [
-                line
-                for line in err.strip().splitlines()
-                if expected_runtime_warning not in line
-            ]
-            self.assertEqual(filtered_err_lines, [])
-        else:
-            self.assertEqual(err, "")
+        self.assertEqual(self._nogil_filtered_err(err, "embedded_ext"), "")
         self.assertEqual(out,
                          "<module 'my_test_extension' (static-extension)>\n"
                          "my_test_extension.executed='yes'\n"
@@ -264,6 +250,26 @@ def test_create_module_from_initfunc(self):
                          "embedded_ext.executed='yes'\n"
                          )
 
+    def test_inittab_submodule_multiphase(self):
+        out, err = self.run_embedded_interpreter("test_inittab_submodule_multiphase")
+        self.assertEqual(err, "")
+        self.assertEqual(out,
+                         "<module 'mp_pkg.mp_submod' (built-in)>\n"
+                         "<module 'mp_pkg.mp_submod' (built-in)>\n"
+                         "Hello from sub-module\n"
+                         "mp_pkg.mp_submod.mp_submod_exec_slot_ran='yes'\n"
+                         "mp_pkg.mp_pkg_exec_slot_ran='yes'\n"
+                         )
+
+    def test_inittab_submodule_singlephase(self):
+        out, err = self.run_embedded_interpreter("test_inittab_submodule_singlephase")
+        self.assertEqual(self._nogil_filtered_err(err, "sp_pkg"), "")
+        self.assertEqual(out,
+                         "<module 'sp_pkg.sp_submod' (built-in)>\n"
+                         "<module 'sp_pkg.sp_submod' (built-in)>\n"
+                         "Hello from sub-module\n"
+                         )
+
     def test_forced_io_encoding(self):
         # Checks forced configuration of embedded interpreter IO streams
         env = dict(os.environ, PYTHONIOENCODING="utf-8:surrogateescape")
@@ -541,6 +547,24 @@ def test_getargs_reset_static_parser(self):
         out, err = self.run_embedded_interpreter("test_repeated_init_exec", code)
         self.assertEqual(out, '1\n2\n3\n' * INIT_LOOPS)
 
+    @staticmethod
+    def _nogil_filtered_err(err: str, mod_name: str) -> str:
+        if not support.Py_GIL_DISABLED:
+            return err
+
+        # the test imports a singlephase init extension, so it emits a warning
+        # under the free-threaded build
+        expected_runtime_warning = (
+            "RuntimeWarning: The global interpreter lock (GIL)"
+            f" has been enabled to load module '{mod_name}'"
+        )
+        filtered_err_lines = [
+            line
+            for line in err.strip().splitlines()
+            if expected_runtime_warning not in line
+        ]
+        return "\n".join(filtered_err_lines)
+
 
 def config_dev_mode(preconfig, config):
     preconfig['allocator'] = PYMEM_ALLOCATOR_DEBUG

diff --git a/Programs/_testembed.c b/Programs/_testembed.c
@@ -2323,6 +2323,177 @@ test_create_module_from_initfunc(void)
     return Py_RunMain();
 }
 
+/// Multi-phase initialization package & submodule ///
+
+int
+mp_pkg_exec(PyObject *mod)
+{
+    // make this a namespace package
+    // empty list = namespace package
+    if (PyModule_Add(mod, "__path__", PyList_New(0)) < 0) {
+        return -1;
+    }
+    if (PyModule_AddStringConstant(mod, "mp_pkg_exec_slot_ran", "yes") < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+static PyModuleDef_Slot mp_pkg_slots[] = {
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {Py_mod_exec, mp_pkg_exec},
+    {0, NULL}
+};
+
+static struct PyModuleDef mp_pkg_def = {
+    PyModuleDef_HEAD_INIT,
+    .m_name = "mp_pkg",
+    .m_size = 0,
+    .m_slots = mp_pkg_slots,
+};
+
+PyMODINIT_FUNC
+PyInit_mp_pkg(void)
+{
+    return PyModuleDef_Init(&mp_pkg_def);
+}
+
+static PyObject *
+submod_greet(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return PyUnicode_FromString("Hello from sub-module");
+}
+
+static PyMethodDef submod_methods[] = {
+    {"greet", submod_greet, METH_NOARGS, NULL},
+    {NULL},
+};
+
+int
+mp_submod_exec(PyObject *mod)
+{
+    return PyModule_AddStringConstant(mod, "mp_submod_exec_slot_ran", "yes");
+}
+
+static PyModuleDef_Slot mp_submod_slots[] = {
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {Py_mod_exec, mp_submod_exec},
+    {0, NULL}
+};
+
+static struct PyModuleDef mp_submod_def = {
+    PyModuleDef_HEAD_INIT,
+    .m_name = "mp_pkg.mp_submod",
+    .m_size = 0,
+    .m_methods = submod_methods,
+    .m_slots = mp_submod_slots,
+};
+
+PyMODINIT_FUNC
+PyInit_mp_submod(void)
+{
+    return PyModuleDef_Init(&mp_submod_def);
+}
+
+static int
+test_inittab_submodule_multiphase(void)
+{
+    wchar_t* argv[] = {
+        PROGRAM_NAME,
+        L"-c",
+        L"import sys;"
+        L"import mp_pkg.mp_submod;"
+        L"print(mp_pkg.mp_submod);"
+        L"print(sys.modules['mp_pkg.mp_submod']);"
+        L"print(mp_pkg.mp_submod.greet());"
+        L"print(f'{mp_pkg.mp_submod.mp_submod_exec_slot_ran=}');"
+        L"print(f'{mp_pkg.mp_pkg_exec_slot_ran=}');"
+    };
+    PyConfig config;
+    if (PyImport_AppendInittab("mp_pkg",
+                               &PyInit_mp_pkg) != 0) {
+        fprintf(stderr, "PyImport_AppendInittab() failed\n");
+        return 1;
+    }
+    if (PyImport_AppendInittab("mp_pkg.mp_submod",
+                               &PyInit_mp_submod) != 0) {
+        fprintf(stderr, "PyImport_AppendInittab() failed\n");
+        return 1;
+    }
+    PyConfig_InitPythonConfig(&config);
+    config.isolated = 1;
+    config_set_argv(&config, Py_ARRAY_LENGTH(argv), argv);
+    init_from_config_clear(&config);
+    return Py_RunMain();
+}
+
+/// Single-phase initialization package & submodule ///
+
+static struct PyModuleDef sp_pkg_def = {
+    PyModuleDef_HEAD_INIT,
+    .m_name = "sp_pkg",
+    .m_size = 0,
+};
+
+PyMODINIT_FUNC
+PyInit_sp_pkg(void)
+{
+    PyObject *mod = PyModule_Create(&sp_pkg_def);
+    if (mod == NULL) {
+        return NULL;
+    }
+    // make this a namespace package
+    // empty list = namespace package
+    if (PyModule_Add(mod, "__path__", PyList_New(0)) < 0) {
+        Py_DECREF(mod);
+        return NULL;
+    }
+    return mod;
+}
+
+static struct PyModuleDef sp_submod_def = {
+    PyModuleDef_HEAD_INIT,
+    .m_name = "sp_pkg.sp_submod",
+    .m_size = 0,
+    .m_methods = submod_methods,
+};
+
+PyMODINIT_FUNC
+PyInit_sp_submod(void)
+{
+    return PyModule_Create(&sp_submod_def);
+}
+
+static int
+test_inittab_submodule_singlephase(void)
+{
+    wchar_t* argv[] = {
+        PROGRAM_NAME,
+        L"-c",
+        L"import sys;"
+        L"import sp_pkg.sp_submod;"
+        L"print(sp_pkg.sp_submod);"
+        L"print(sys.modules['sp_pkg.sp_submod']);"
+        L"print(sp_pkg.sp_submod.greet());"
+    };
+    PyConfig config;
+    if (PyImport_AppendInittab("sp_pkg",
+                               &PyInit_sp_pkg) != 0) {
+        fprintf(stderr, "PyImport_AppendInittab() failed\n");
+        return 1;
+    }
+    if (PyImport_AppendInittab("sp_pkg.sp_submod",
+                               &PyInit_sp_submod) != 0) {
+        fprintf(stderr, "PyImport_AppendInittab() failed\n");
+        return 1;
+    }
+    PyConfig_InitPythonConfig(&config);
+    config.isolated = 1;
+    config_set_argv(&config, Py_ARRAY_LENGTH(argv), argv);
+    init_from_config_clear(&config);
+    return Py_RunMain();
+}
+
 static void wrap_allocator(PyMemAllocatorEx *allocator);
 static void unwrap_allocator(PyMemAllocatorEx *allocator);
 
@@ -2507,6 +2678,8 @@ static struct TestCase TestCases[] = {
     {"test_get_incomplete_frame", test_get_incomplete_frame},
     {"test_gilstate_after_finalization", test_gilstate_after_finalization},
     {"test_create_module_from_initfunc", test_create_module_from_initfunc},
+    {"test_inittab_submodule_multiphase", test_inittab_submodule_multiphase},
+    {"test_inittab_submodule_singlephase", test_inittab_submodule_singlephase},
     {NULL, NULL}
 };
 

@@ -156,7 +156,6 @@ _Py_ext_module_loader_info_init_for_builtin(
                             PyObject *name)
 {
     assert(PyUnicode_Check(name));
-    assert(PyUnicode_FindChar(name, '.', 0, PyUnicode_GetLength(name), -1) == -1);
     assert(PyUnicode_GetLength(name) > 0);
 
     PyObject *name_encoded = PyUnicode_AsEncodedString(name, "ascii", NULL);