bpo-42260: Add _PyInterpreterState_SetConfig() (GH-23158)

* Inline _PyInterpreterState_SetConfig(): replace it with
  _PyConfig_Copy().
* Add _PyErr_SetFromPyStatus()
* Add _PyInterpreterState_GetConfigCopy()
* Add a new _PyInterpreterState_SetConfig() function.
* Add an unit which gets, modifies, and sets the config.

Doc/c-api/init_config.rst

@@ -128,6 +128,8 @@ PyStatus
 
       Initialization error with a message.
 
+      *err_msg* must not be ``NULL``.
+
    .. c:function:: PyStatus PyStatus_NoMemory(void)
 
       Memory allocation failure (out of memory).

Include/cpython/pystate.h

@@ -193,6 +193,36 @@ PyAPI_FUNC(void) _PyInterpreterState_SetEvalFrameFunc(
 
 PyAPI_FUNC(const PyConfig*) _PyInterpreterState_GetConfig(PyInterpreterState *interp);
 
+/* Get a copy of the current interpreter configuration.
+
+   Return 0 on success. Raise an exception and return -1 on error.
+
+   The caller must initialize 'config', using PyConfig_InitPythonConfig()
+   for example.
+
+   Python must be preinitialized to call this method.
+   The caller must hold the GIL. */
+PyAPI_FUNC(int) _PyInterpreterState_GetConfigCopy(
+    struct PyConfig *config);
+
+/* Set the configuration of the current interpreter.
+
+   This function should be called during or just after the Python
+   initialization.
+
+   Update the sys module with the new configuration. If the sys module was
+   modified directly after the Python initialization, these changes are lost.
+
+   Some configuration like faulthandler or warnoptions can be updated in the
+   configuration, but don't reconfigure Python (don't enable/disable
+   faulthandler and don't reconfigure warnings filters).
+
+   Return 0 on success. Raise an exception and return -1 on error.
+
+   The configuration should come from _PyInterpreterState_GetConfigCopy(). */
+PyAPI_FUNC(int) _PyInterpreterState_SetConfig(
+    const struct PyConfig *config);
+
 // Get the configuration of the currrent interpreter.
 // The caller must hold the GIL.
 PyAPI_FUNC(const PyConfig*) _Py_GetConfig(void);

Include/internal/pycore_initconfig.h

@@ -44,6 +44,8 @@ struct pyruntimestate;
 #define _PyStatus_UPDATE_FUNC(err) \
     do { err.func = _PyStatus_GET_FUNC(); } while (0)
 
+PyObject* _PyErr_SetFromPyStatus(PyStatus status);
+
 /* --- PyWideStringList ------------------------------------------------ */
 
 #define _PyWideStringList_INIT (PyWideStringList){.length = 0, .items = NULL}

Include/internal/pycore_interp.h

@@ -263,13 +263,7 @@ struct _is {
     struct ast_state ast;
 };
 
-/* Used by _PyImport_Cleanup() */
 extern void _PyInterpreterState_ClearModules(PyInterpreterState *interp);
-
-extern PyStatus _PyInterpreterState_SetConfig(
-    PyInterpreterState *interp,
-    const PyConfig *config);
-
 extern void _PyInterpreterState_Clear(PyThreadState *tstate);
 
 

Lib/test/test_embed.py

@@ -1394,6 +1394,15 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
         self.check_all_configs("test_init_warnoptions", config, preconfig,
                                api=API_PYTHON)
 
+    def test_init_set_config(self):
+        config = {
+            '_init_main': 0,
+            'bytes_warning': 2,
+            'warnoptions': ['error::BytesWarning'],
+        }
+        self.check_all_configs("test_init_set_config", config,
+                               api=API_ISOLATED)
+
     def test_get_argc_argv(self):
         self.run_embedded_interpreter("test_get_argc_argv")
         # ignore output

Programs/_testembed.c

@@ -1526,6 +1526,55 @@ static int test_init_warnoptions(void)
 }
 
 
+static int tune_config(void)
+{
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    if (_PyInterpreterState_GetConfigCopy(&config) < 0) {
+        PyConfig_Clear(&config);
+        PyErr_Print();
+        return -1;
+    }
+
+    config.bytes_warning = 2;
+
+    if (_PyInterpreterState_SetConfig(&config) < 0) {
+        PyConfig_Clear(&config);
+        return -1;
+    }
+    PyConfig_Clear(&config);
+    return 0;
+}
+
+
+static int test_set_config(void)
+{
+    // Initialize core
+    PyConfig config;
+    PyConfig_InitIsolatedConfig(&config);
+    config_set_string(&config, &config.program_name, PROGRAM_NAME);
+    config._init_main = 0;
+    config.bytes_warning = 0;
+    init_from_config_clear(&config);
+
+    // Tune the configuration using _PyInterpreterState_SetConfig()
+    if (tune_config() < 0) {
+        PyErr_Print();
+        return 1;
+    }
+
+    // Finish initialization: main part
+    PyStatus status = _Py_InitializeMain();
+    if (PyStatus_Exception(status)) {
+        Py_ExitStatusException(status);
+    }
+
+    dump_config();
+    Py_Finalize();
+    return 0;
+}
+
+
 static void configure_init_main(PyConfig *config)
 {
     wchar_t* argv[] = {
@@ -1693,6 +1742,7 @@ static struct TestCase TestCases[] = {
     {"test_init_setpath_config", test_init_setpath_config},
     {"test_init_setpythonhome", test_init_setpythonhome},
     {"test_init_warnoptions", test_init_warnoptions},
+    {"test_init_set_config", test_set_config},
     {"test_run_main", test_run_main},
     {"test_get_argc_argv", test_get_argc_argv},
 

Python/initconfig.c

@@ -242,6 +242,7 @@ PyStatus PyStatus_Ok(void)
 
 PyStatus PyStatus_Error(const char *err_msg)
 {
+    assert(err_msg != NULL);
     return (PyStatus){._type = _PyStatus_TYPE_ERROR,
                       .err_msg = err_msg};
 }
@@ -262,6 +263,23 @@ int PyStatus_IsExit(PyStatus status)
 int PyStatus_Exception(PyStatus status)
 { return _PyStatus_EXCEPTION(status); }
 
+PyObject*
+_PyErr_SetFromPyStatus(PyStatus status)
+{
+    if (!_PyStatus_IS_ERROR(status)) {
+        PyErr_Format(PyExc_SystemError,
+                     "%s() expects an error PyStatus",
+                     _PyStatus_GET_FUNC());
+    }
+    else if (status.func) {
+        PyErr_Format(PyExc_ValueError, "%s: %s", status.func, status.err_msg);
+    }
+    else {
+        PyErr_Format(PyExc_ValueError, "%s", status.err_msg);
+    }
+    return NULL;
+}
+
 
 /* --- PyWideStringList ------------------------------------------------ */
 

Python/pylifecycle.c

@@ -428,6 +428,67 @@ _Py_SetLocaleFromEnv(int category)
 }
 
 
+static int
+interpreter_set_config(const PyConfig *config)
+{
+    PyThreadState *tstate = PyThreadState_Get();
+
+    PyStatus status = _PyConfig_Write(config, tstate->interp->runtime);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyErr_SetFromPyStatus(status);
+        return -1;
+    }
+
+    status = _PyConfig_Copy(&tstate->interp->config, config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyErr_SetFromPyStatus(status);
+        return -1;
+    }
+    config = &tstate->interp->config;
+
+    if (config->_install_importlib && _Py_IsMainInterpreter(tstate)) {
+        status = _PyConfig_WritePathConfig(config);
+        if (_PyStatus_EXCEPTION(status)) {
+            _PyErr_SetFromPyStatus(status);
+            return -1;
+        }
+    }
+
+    // Update the sys module for the new configuration
+    if (_PySys_UpdateConfig(tstate) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+
+int
+_PyInterpreterState_SetConfig(const PyConfig *src_config)
+{
+    int res = -1;
+
+    PyConfig config;
+    PyConfig_InitPythonConfig(&config);
+    PyStatus status = _PyConfig_Copy(&config, src_config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyErr_SetFromPyStatus(status);
+        goto done;
+    }
+
+    status = PyConfig_Read(&config);
+    if (_PyStatus_EXCEPTION(status)) {
+        _PyErr_SetFromPyStatus(status);
+        goto done;
+    }
+
+    res = interpreter_set_config(&config);
+
+done:
+    PyConfig_Clear(&config);
+    return res;
+}
+
+
 /* Global initializations.  Can be undone by Py_Finalize().  Don't
    call this twice without an intervening Py_Finalize() call.
 
@@ -462,7 +523,7 @@ pyinit_core_reconfigure(_PyRuntimeState *runtime,
         return status;
     }
 
-    status = _PyInterpreterState_SetConfig(interp, config);
+    status = _PyConfig_Copy(&interp->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
@@ -550,7 +611,7 @@ pycore_create_interpreter(_PyRuntimeState *runtime,
         return _PyStatus_ERR("can't make main interpreter");
     }
 
-    PyStatus status = _PyInterpreterState_SetConfig(interp, config);
+    PyStatus status = _PyConfig_Copy(&interp->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
@@ -917,7 +978,7 @@ pyinit_core(_PyRuntimeState *runtime,
     }
 
     PyConfig config;
-    _PyConfig_InitCompatConfig(&config);
+    PyConfig_InitPythonConfig(&config);
 
     status = _PyConfig_Copy(&config, src_config);
     if (_PyStatus_EXCEPTION(status)) {
@@ -1835,7 +1896,8 @@ new_interpreter(PyThreadState **tstate_p, int isolated_subinterpreter)
         config = _PyInterpreterState_GetConfig(main_interp);
     }
 
-    status = _PyInterpreterState_SetConfig(interp, config);
+
+    status = _PyConfig_Copy(&interp->config, config);
     if (_PyStatus_EXCEPTION(status)) {
         goto error;
     }

Python/pystate.c

@@ -778,7 +778,7 @@ PyState_RemoveModule(struct PyModuleDef* def)
     return PyList_SetItem(interp->modules_by_index, index, Py_None);
 }
 
-/* Used by PyImport_Cleanup() */
+// Used by finalize_modules()
 void
 _PyInterpreterState_ClearModules(PyInterpreterState *interp)
 {
@@ -1920,11 +1920,17 @@ _PyInterpreterState_GetConfig(PyInterpreterState *interp)
 }
 
 
-PyStatus
-_PyInterpreterState_SetConfig(PyInterpreterState *interp,
-                              const PyConfig *config)
+int
+_PyInterpreterState_GetConfigCopy(PyConfig *config)
 {
-    return _PyConfig_Copy(&interp->config, config);
+    PyInterpreterState *interp = PyInterpreterState_Get();
+
+    PyStatus status = _PyConfig_Copy(config, &interp->config);
+    if (PyStatus_Exception(status)) {
+        _PyErr_SetFromPyStatus(status);
+        return -1;
+    }
+    return 0;
 }