gh-107954, PEP 741: Add PyInitConfig_AddModule() function (#123668)

Doc/c-api/init_config.rst

@@ -1744,6 +1744,26 @@ only implemented when ``Py_InitializeFromInitConfig()`` is called, not by the
    * Set an error in *config* and return ``-1`` on error.
 
 
+Module
+------
+
+.. c:function:: int PyInitConfig_AddModule(PyInitConfig *config, const char *name, PyObject* (*initfunc)(void))
+
+   Add a built-in extension module to the table of built-in modules.
+
+   The new module can be imported by the name *name*, and uses the function
+   *initfunc* as the initialization function called on the first attempted
+   import.
+
+   * Return ``0`` on success.
+   * Set an error in *config* and return ``-1`` on error.
+
+   If Python is initialized multiple times, ``PyInitConfig_AddModule()`` must
+   be called at each Python initialization.
+
+   Similar to the :c:func:`PyImport_AppendInittab` function.
+
+
 Initialize Python
 -----------------
 

Doc/whatsnew/3.14.rst

@@ -524,6 +524,7 @@ New Features
   * :c:func:`PyInitConfig_SetInt`
   * :c:func:`PyInitConfig_SetStr`
   * :c:func:`PyInitConfig_SetStrList`
+  * :c:func:`PyInitConfig_AddModule`
   * :c:func:`Py_InitializeFromInitConfig`
 
   (Contributed by Victor Stinner in :gh:`107954`.)

Include/cpython/initconfig.h

@@ -313,6 +313,10 @@ PyAPI_FUNC(int) PyInitConfig_SetStrList(PyInitConfig *config,
     size_t length,
     char * const *items);
 
+PyAPI_FUNC(int) PyInitConfig_AddModule(PyInitConfig *config,
+    const char *name,
+    PyObject* (*initfunc)(void));
+
 PyAPI_FUNC(int) Py_InitializeFromInitConfig(PyInitConfig *config);
 
 

Lib/test/test_embed.py

@@ -1775,6 +1775,9 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
     def test_initconfig_exit(self):
         self.run_embedded_interpreter("test_initconfig_exit")
 
+    def test_initconfig_module(self):
+        self.run_embedded_interpreter("test_initconfig_module")
+
     def test_get_argc_argv(self):
         self.run_embedded_interpreter("test_get_argc_argv")
         # ignore output

Misc/NEWS.d/next/C_API/2024-08-30-14-02-17.gh-issue-107954.TPvj4u.rst

@@ -12,6 +12,7 @@ Add functions to configure the Python initialization (:pep:`741`):
 * :c:func:`PyInitConfig_SetInt`
 * :c:func:`PyInitConfig_SetStr`
 * :c:func:`PyInitConfig_SetStrList`
+* :c:func:`PyInitConfig_AddModule`
 * :c:func:`Py_InitializeFromInitConfig`
 
 Patch by Victor Stinner.

Programs/_testembed.c

@@ -1963,6 +1963,62 @@ static int test_initconfig_exit(void)
 }
 
 
+static PyModuleDef_Slot extension_slots[] = {
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {0, NULL}
+};
+
+static struct PyModuleDef extension_module = {
+    PyModuleDef_HEAD_INIT,
+    .m_name = "my_test_extension",
+    .m_size = 0,
+    .m_slots = extension_slots,
+};
+
+static PyObject* init_my_test_extension(void)
+{
+    return PyModuleDef_Init(&extension_module);
+}
+
+
+static int test_initconfig_module(void)
+{
+    PyInitConfig *config = PyInitConfig_Create();
+    if (config == NULL) {
+        printf("Init allocation error\n");
+        return 1;
+    }
+
+    if (PyInitConfig_SetStr(config, "program_name", PROGRAM_NAME_UTF8) < 0) {
+        goto error;
+    }
+
+    if (PyInitConfig_AddModule(config, "my_test_extension",
+                               init_my_test_extension) < 0) {
+        goto error;
+    }
+
+    if (Py_InitializeFromInitConfig(config) < 0) {
+        goto error;
+    }
+    PyInitConfig_Free(config);
+
+    if (PyRun_SimpleString("import my_test_extension") < 0) {
+        fprintf(stderr, "unable to import my_test_extension\n");
+        exit(1);
+    }
+
+    Py_Finalize();
+    return 0;
+
+    const char *err_msg;
+error:
+    (void)PyInitConfig_GetError(config, &err_msg);
+    printf("Python init failed: %s\n", err_msg);
+    exit(1);
+}
+
+
 static void configure_init_main(PyConfig *config)
 {
     wchar_t* argv[] = {
@@ -2384,6 +2440,7 @@ static struct TestCase TestCases[] = {
     {"test_initconfig_api", test_initconfig_api},
     {"test_initconfig_get_api", test_initconfig_get_api},
     {"test_initconfig_exit", test_initconfig_exit},
+    {"test_initconfig_module", test_initconfig_module},
     {"test_run_main", test_run_main},
     {"test_run_main_loop", test_run_main_loop},
     {"test_get_argc_argv", test_get_argc_argv},

Python/initconfig.c

@@ -3423,6 +3423,8 @@ _Py_DumpPathConfig(PyThreadState *tstate)
 struct PyInitConfig {
     PyPreConfig preconfig;
     PyConfig config;
+    struct _inittab *inittab;
+    Py_ssize_t inittab_size;
     PyStatus status;
     char *err_msg;
 };
@@ -3873,9 +3875,42 @@ PyInitConfig_SetStrList(PyInitConfig *config, const char *name,
 }
 
 
+int
+PyInitConfig_AddModule(PyInitConfig *config, const char *name,
+                       PyObject* (*initfunc)(void))
+{
+    size_t size = sizeof(struct _inittab) * (config->inittab_size + 2);
+    struct _inittab *new_inittab = PyMem_RawRealloc(config->inittab, size);
+    if (new_inittab == NULL) {
+        config->status = _PyStatus_NO_MEMORY();
+        return -1;
+    }
+    config->inittab = new_inittab;
+
+    struct _inittab *entry = &config->inittab[config->inittab_size];
+    entry->name = name;
+    entry->initfunc = initfunc;
+
+    // Terminator entry
+    entry = &config->inittab[config->inittab_size + 1];
+    entry->name = NULL;
+    entry->initfunc = NULL;
+
+    config->inittab_size++;
+    return 0;
+}
+
+
 int
 Py_InitializeFromInitConfig(PyInitConfig *config)
 {
+    if (config->inittab_size >= 1) {
+        if (PyImport_ExtendInittab(config->inittab) < 0) {
+            config->status = _PyStatus_NO_MEMORY();
+            return -1;
+        }
+    }
+
     _PyPreConfig_GetConfig(&config->preconfig, &config->config);
 
     config->status = Py_PreInitializeFromArgs(