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gh-142417: Add PyInitConfig_SetInitCallback() function#142420

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vstinner wants to merge4 commits intopython:mainfromvstinner:init_callback
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37 changes: 37 additions & 0 deletionsDoc/c-api/init_config.rst
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Expand Up@@ -238,6 +238,43 @@ Module
Similar to the :c:func:`PyImport_AppendInittab` function.


Initialization Callback
-----------------------

.. c:function:: int PyInitConfig_SetInitCallback(PyInitConfig *config, PyStatus (*callback)(void *arg), void *arg)

Set an initialization callback. It allows executing code during the
Python interpreter, before the first import. For example, it
can be used to add a meta path importer into :data:`sys.meta_path`.

When the callback is called, Python is only partially initialized. What's
available at this point:

* Builtin types;
* Builtin exceptions;
* Builtin and frozen modules (can be imported);
* The :mod:`sys` module is only partially initialized
(ex: :data:`sys.path` and :data:`sys.stdout` don't exist yet).

After the callback, the Python initialization is completed:

* Install and configure :mod:`importlib`;
* Apply the :ref:`Path Configuration <init-path-config>`;
* Install signal handlers;
* Finish :mod:`sys` module initialization (ex: create :data:`sys.stdout`
and :data:`sys.path`);
* Enable optional features like :mod:`faulthandler` and :mod:`tracemalloc`;
* Import the :mod:`site` module;
* etc.

A single callback can be registered. If this function is called more than
once, it fails with an error.

* Return ``0`` on success.
* Set an error in *config* and return ``-1`` on error.

.. versionadded:: next

Initialize Python
-----------------

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5 changes: 5 additions & 0 deletionsDoc/whatsnew/3.15.rst
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Expand Up@@ -1228,6 +1228,11 @@ New features
a module from a *spec* and *initfunc*.
(Contributed by Itamar Oren in :gh:`116146`.)

* Add :c:func:`PyInitConfig_SetInitCallback` to execute code as soon as the
Python interpreter is initialized, before the first import. For example, it
can be used to add a meta path importer into :data:`sys.meta_path`.
(Contributed by Victor Stinner in :gh:`142417`.)

* Add :c:func:`PyTuple_FromArray` to create a :class:`tuple` from an array.
(Contributed by Victor Stinner in :gh:`111489`.)

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10 changes: 10 additions & 0 deletionsInclude/cpython/initconfig.h
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Expand Up@@ -215,6 +215,12 @@ typedef struct PyConfig {
wchar_t *run_module;
wchar_t *run_filename;

/* --- Initialization callback ------------------- */

// See PyInitConfig_SetInitCallback() function.
PyStatus (*init_callback)(void *arg);
void *init_callback_arg;

/* --- Set by Py_Main() -------------------------- */
wchar_t *sys_path_0;

Expand DownExpand Up@@ -323,6 +329,10 @@ PyAPI_FUNC(int) PyInitConfig_AddModule(PyInitConfig *config,
const char *name,
PyObject* (*initfunc)(void));

PyAPI_FUNC(int) PyInitConfig_SetInitCallback(PyInitConfig *config,
PyStatus (*callback)(void *arg),
void *arg);

PyAPI_FUNC(int) Py_InitializeFromInitConfig(PyInitConfig *config);


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14 changes: 14 additions & 0 deletionsLib/test/test_embed.py
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Expand Up@@ -1885,6 +1885,20 @@ def test_init_in_background_thread(self):
out, err = self.run_embedded_interpreter("test_init_in_background_thread")
self.assertEqual(err, "")

def test_init_callback(self):
out, err = self.run_embedded_interpreter("test_init_callback")
modules = [
'_frozen_importlib', '_imp', '_thread', '_warnings', '_weakref',
'builtins', 'sys']
meta_path = (
"[<class '_frozen_importlib.BuiltinImporter'>, "
"<class '_frozen_importlib.FrozenImporter'>]")
self.assertEqual(err.splitlines(),
["Hello Callback!",
f"sys.modules: {modules}",
f"sys.meta_path: {meta_path}"])
self.assertEqual(out, "")


class AuditingTests(EmbeddingTestsMixin, unittest.TestCase):
def test_open_code_hook(self):
Expand Down
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@@ -0,0 +1,4 @@
Add :c:func:`PyInitConfig_SetInitCallback` to execute code as soon as the
Python interpreter is initialized, before the first import. For example, it can
be used to add a meta path importer into :data:`sys.meta_path`. Patch by Victor
Stinner.
100 changes: 88 additions & 12 deletionsPrograms/_testembed.c
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Expand Up@@ -1741,6 +1741,16 @@ static int initconfig_getint(PyInitConfig *config, const char *name)
return (int)value;
}

static void initconfig_error(PyInitConfig *config)
{
const char *err_msg;
int res = PyInitConfig_GetError(config, &err_msg);
assert(res == 1);

printf("Python init failed: %s\n", err_msg);
PyInitConfig_Free(config);
}


static int test_initconfig_api(void)
{
Expand DownExpand Up@@ -1795,12 +1805,8 @@ static int test_initconfig_api(void)
return 0;

error:
{
const char *err_msg;
(void)PyInitConfig_GetError(config, &err_msg);
printf("Python init failed: %s\n", err_msg);
exit(1);
}
initconfig_error(config);
return 1;
}


Expand DownExpand Up@@ -1953,12 +1959,8 @@ static int test_initconfig_module(void)
return 0;

error:
{
const char *err_msg;
(void)PyInitConfig_GetError(config, &err_msg);
printf("Python init failed: %s\n", err_msg);
exit(1);
}
initconfig_error(config);
return 1;
}


Expand DownExpand Up@@ -2175,6 +2177,79 @@ static int test_init_in_background_thread(void)
}


static PyStatus init_callback(void *arg)
{
const char *msg = (const char*)arg;
fprintf(stderr, "%s\n", msg);

// Write sorted(sys.modules) to sys.stderr
PyObject *modules = PySys_GetAttrString("modules");
if (modules == NULL) {
return PyStatus_Error("failed to get sys.modules");
}

PyObject *builtins = PyEval_GetBuiltins(); // borrowed ref
if (builtins == NULL) {
Py_DECREF(modules);
return PyStatus_Error("failed to get builtins");
}

PyObject *sorted;
if (PyDict_GetItemStringRef(builtins, "sorted", &sorted) <= 0) {
Py_DECREF(modules);
return PyStatus_Error("failed to get sorted");
}

PyObject *names = PyObject_CallOneArg(sorted, modules);
Py_DECREF(modules);
if (names == NULL) {
return PyStatus_Error("sorted failed");
}

PySys_FormatStderr("sys.modules: %R\n", names);
Py_DECREF(names);

// Write sys.meta_path to sys.stderr
const char *code = (
"import sys; "
"print(f\"sys.meta_path: {sys.meta_path}\", file=sys.stderr)");
if (PyRun_SimpleString(code) < 0) {
return PyStatus_Error("PyRun_SimpleString failed");
}

return PyStatus_Ok();
}


static int test_init_callback(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;
}

const char *msg = "Hello Callback!";
if (PyInitConfig_SetInitCallback(config, init_callback, (void*)msg) < 0) {
goto error;
}

if (Py_InitializeFromInitConfig(config) < 0) {
goto error;
}
PyInitConfig_Free(config);
return 0;

error:
initconfig_error(config);
return 1;
}


#ifndef MS_WINDOWS
#include "test_frozenmain.h" // M_test_frozenmain

Expand DownExpand Up@@ -2663,6 +2738,7 @@ static struct TestCase TestCases[] = {
{"test_init_use_frozen_modules", test_init_use_frozen_modules},
{"test_init_main_interpreter_settings", test_init_main_interpreter_settings},
{"test_init_in_background_thread", test_init_in_background_thread},
{"test_init_callback", test_init_callback},

// Audit
{"test_open_code_hook", test_open_code_hook},
Expand Down
19 changes: 19 additions & 0 deletionsPython/initconfig.c
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Expand Up@@ -1274,6 +1274,10 @@ _PyConfig_Copy(PyConfig *config, const PyConfig *config2)
Py_UNREACHABLE();
}
}

config->init_callback = config2->init_callback;
config->init_callback_arg = config2->init_callback_arg;

return _PyStatus_OK();
}

Expand DownExpand Up@@ -4242,6 +4246,21 @@ Py_InitializeFromInitConfig(PyInitConfig *config)
}


int
PyInitConfig_SetInitCallback(PyInitConfig *config,
PyStatus (*callback)(void *arg), void *arg)
{
if (config->config.init_callback != NULL) {
initconfig_set_error(config, "cannot set two init callbacks");
return -1;
}

config->config.init_callback = callback;
config->config.init_callback_arg = arg;
return 0;
}


// --- PyConfig_Get() -------------------------------------------------------

static const PyConfigSpec*
Expand Down
7 changes: 7 additions & 0 deletionsPython/pylifecycle.c
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Expand Up@@ -1462,6 +1462,13 @@ Py_InitializeFromConfig(const PyConfig *config)
}
config = _PyInterpreterState_GetConfig(tstate->interp);

if (config->init_callback != NULL) {
status = config->init_callback(config->init_callback_arg);
if (_PyStatus_EXCEPTION(status)) {
return status;
}
}

if (config->_init_main) {
status = pyinit_main(tstate);
if (_PyStatus_EXCEPTION(status)) {
Expand Down
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