gh-107954, PEP 741: Add PyConfig_Get()/Set() functions (#123472)

Add PyConfig_Get(), PyConfig_GetInt(), PyConfig_Set() and
PyConfig_Names() functions to get and set the current runtime Python
configuration.

Add visibility and "sys spec" to config and preconfig specifications.

_PyConfig_AsDict() now converts PyConfig.xoptions as a dictionary.

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

2 files changed, 844 insertions, 194 deletions

diff --git a/Python/initconfig.c b/Python/initconfig.c
index 51897a2..1c21486 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -10,6 +10,7 @@
 #include "pycore_pymem.h"         // _PyMem_SetDefaultAllocator()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 #include "pycore_pystats.h"       // _Py_StatsOn()
+#include "pycore_sysmodule.h"     // _PySys_SetIntMaxStrDigits()
 
 #include "osdefs.h"               // DELIM
 
@@ -26,6 +27,22 @@
 
 #include "config_common.h"
 
+/* --- PyConfig setters ------------------------------------------- */
+
+typedef PyObject* (*config_sys_flag_setter) (int value);
+
+static PyObject*
+config_sys_flag_long(int value)
+{
+    return PyLong_FromLong(value);
+}
+
+static PyObject*
+config_sys_flag_not(int value)
+{
+    value = (!value);
+    return config_sys_flag_long(value);
+}
 
 /* --- PyConfig spec ---------------------------------------------- */
 
@@ -40,99 +57,174 @@ typedef enum {
     PyConfig_MEMBER_WSTR_LIST = 12,
 } PyConfigMemberType;
 
+typedef enum {
+    // Option which cannot be get or set by PyConfig_Get() and PyConfig_Set()
+    PyConfig_MEMBER_INIT_ONLY = 0,
+
+    // Option which cannot be set by PyConfig_Set()
+    PyConfig_MEMBER_READ_ONLY = 1,
+
+    // Public option: can be get and set by PyConfig_Get() and PyConfig_Set()
+    PyConfig_MEMBER_PUBLIC = 2,
+} PyConfigMemberVisibility;
+
+typedef struct {
+    const char *attr;
+    int flag_index;
+    config_sys_flag_setter flag_setter;
+} PyConfigSysSpec;
+
 typedef struct {
     const char *name;
     size_t offset;
     PyConfigMemberType type;
+    PyConfigMemberVisibility visibility;
+    PyConfigSysSpec sys;
 } PyConfigSpec;
 
-#define SPEC(MEMBER, TYPE) \
-    {#MEMBER, offsetof(PyConfig, MEMBER), PyConfig_MEMBER_##TYPE}
+#define SPEC(MEMBER, TYPE, VISIBILITY, sys) \
+    {#MEMBER, offsetof(PyConfig, MEMBER), \
+     PyConfig_MEMBER_##TYPE, PyConfig_MEMBER_##VISIBILITY, sys}
+
+#define SYS_ATTR(name) {name, -1, NULL}
+#define SYS_FLAG_SETTER(index, setter) {NULL, index, setter}
+#define SYS_FLAG(index) SYS_FLAG_SETTER(index, NULL)
+#define NO_SYS SYS_ATTR(NULL)
 
 // Update _test_embed_set_config when adding new members
 static const PyConfigSpec PYCONFIG_SPEC[] = {
-    SPEC(_config_init, UINT),
-    SPEC(isolated, BOOL),
-    SPEC(use_environment, BOOL),
-    SPEC(dev_mode, BOOL),
-    SPEC(install_signal_handlers, BOOL),
-    SPEC(use_hash_seed, BOOL),
-    SPEC(hash_seed, ULONG),
-    SPEC(faulthandler, BOOL),
-    SPEC(tracemalloc, UINT),
-    SPEC(perf_profiling, UINT),
-    SPEC(import_time, BOOL),
-    SPEC(code_debug_ranges, BOOL),
-    SPEC(show_ref_count, BOOL),
-    SPEC(dump_refs, BOOL),
-    SPEC(dump_refs_file, WSTR_OPT),
-    SPEC(malloc_stats, BOOL),
-    SPEC(filesystem_encoding, WSTR),
-    SPEC(filesystem_errors, WSTR),
-    SPEC(pycache_prefix, WSTR_OPT),
-    SPEC(parse_argv, BOOL),
-    SPEC(orig_argv, WSTR_LIST),
-    SPEC(argv, WSTR_LIST),
-    SPEC(xoptions, WSTR_LIST),
-    SPEC(warnoptions, WSTR_LIST),
-    SPEC(site_import, BOOL),
-    SPEC(bytes_warning, UINT),
-    SPEC(warn_default_encoding, BOOL),
-    SPEC(inspect, BOOL),
-    SPEC(interactive, BOOL),
-    SPEC(optimization_level, UINT),
-    SPEC(parser_debug, BOOL),
-    SPEC(write_bytecode, BOOL),
-    SPEC(verbose, UINT),
-    SPEC(quiet, BOOL),
-    SPEC(user_site_directory, BOOL),
-    SPEC(configure_c_stdio, BOOL),
-    SPEC(buffered_stdio, BOOL),
-    SPEC(stdio_encoding, WSTR),
-    SPEC(stdio_errors, WSTR),
-#ifdef MS_WINDOWS
-    SPEC(legacy_windows_stdio, BOOL),
+    // --- Public options -----------
+
+    SPEC(argv, WSTR_LIST, PUBLIC, SYS_ATTR("argv")),
+    SPEC(base_exec_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("base_exec_prefix")),
+    SPEC(base_executable, WSTR_OPT, PUBLIC, SYS_ATTR("_base_executable")),
+    SPEC(base_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("base_prefix")),
+    SPEC(bytes_warning, UINT, PUBLIC, SYS_FLAG(9)),
+    SPEC(exec_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("exec_prefix")),
+    SPEC(executable, WSTR_OPT, PUBLIC, SYS_ATTR("executable")),
+    SPEC(inspect, BOOL, PUBLIC, SYS_FLAG(1)),
+    SPEC(int_max_str_digits, UINT, PUBLIC, NO_SYS),
+    SPEC(interactive, BOOL, PUBLIC, SYS_FLAG(2)),
+    SPEC(module_search_paths, WSTR_LIST, PUBLIC, SYS_ATTR("path")),
+    SPEC(optimization_level, UINT, PUBLIC, SYS_FLAG(3)),
+    SPEC(parser_debug, BOOL, PUBLIC, SYS_FLAG(0)),
+    SPEC(platlibdir, WSTR, PUBLIC, SYS_ATTR("platlibdir")),
+    SPEC(prefix, WSTR_OPT, PUBLIC, SYS_ATTR("prefix")),
+    SPEC(pycache_prefix, WSTR_OPT, PUBLIC, SYS_ATTR("pycache_prefix")),
+    SPEC(quiet, BOOL, PUBLIC, SYS_FLAG(10)),
+    SPEC(stdlib_dir, WSTR_OPT, PUBLIC, SYS_ATTR("_stdlib_dir")),
+    SPEC(use_environment, BOOL, PUBLIC, SYS_FLAG_SETTER(7, config_sys_flag_not)),
+    SPEC(verbose, UINT, PUBLIC, SYS_FLAG(8)),
+    SPEC(warnoptions, WSTR_LIST, PUBLIC, SYS_ATTR("warnoptions")),
+    SPEC(write_bytecode, BOOL, PUBLIC, SYS_FLAG_SETTER(4, config_sys_flag_not)),
+    SPEC(xoptions, WSTR_LIST, PUBLIC, SYS_ATTR("_xoptions")),
+
+    // --- Read-only options -----------
+
+#ifdef Py_STATS
+    SPEC(_pystats, BOOL, READ_ONLY, NO_SYS),
 #endif
-    SPEC(check_hash_pycs_mode, WSTR),
-    SPEC(use_frozen_modules, BOOL),
-    SPEC(safe_path, BOOL),
-    SPEC(int_max_str_digits, INT),
-    SPEC(cpu_count, INT),
+    SPEC(buffered_stdio, BOOL, READ_ONLY, NO_SYS),
+    SPEC(check_hash_pycs_mode, WSTR, READ_ONLY, NO_SYS),
+    SPEC(code_debug_ranges, BOOL, READ_ONLY, NO_SYS),
+    SPEC(configure_c_stdio, BOOL, READ_ONLY, NO_SYS),
+    SPEC(cpu_count, INT, READ_ONLY, NO_SYS),
+    SPEC(dev_mode, BOOL, READ_ONLY, NO_SYS),  // sys.flags.dev_mode
+    SPEC(dump_refs, BOOL, READ_ONLY, NO_SYS),
+    SPEC(dump_refs_file, WSTR_OPT, READ_ONLY, NO_SYS),
 #ifdef Py_GIL_DISABLED
-    SPEC(enable_gil, INT),
+    SPEC(enable_gil, INT, READ_ONLY, NO_SYS),
 #endif
-    SPEC(pathconfig_warnings, BOOL),
-    SPEC(program_name, WSTR),
-    SPEC(pythonpath_env, WSTR_OPT),
-    SPEC(home, WSTR_OPT),
-    SPEC(platlibdir, WSTR),
-    SPEC(sys_path_0, WSTR_OPT),
-    SPEC(module_search_paths_set, BOOL),
-    SPEC(module_search_paths, WSTR_LIST),
-    SPEC(stdlib_dir, WSTR_OPT),
-    SPEC(executable, WSTR_OPT),
-    SPEC(base_executable, WSTR_OPT),
-    SPEC(prefix, WSTR_OPT),
-    SPEC(base_prefix, WSTR_OPT),
-    SPEC(exec_prefix, WSTR_OPT),
-    SPEC(base_exec_prefix, WSTR_OPT),
-    SPEC(skip_source_first_line, BOOL),
-    SPEC(run_command, WSTR_OPT),
-    SPEC(run_module, WSTR_OPT),
-    SPEC(run_filename, WSTR_OPT),
-    SPEC(_install_importlib, BOOL),
-    SPEC(_init_main, BOOL),
-    SPEC(_is_python_build, BOOL),
-#ifdef Py_STATS
-    SPEC(_pystats, BOOL),
+    SPEC(faulthandler, BOOL, READ_ONLY, NO_SYS),
+    SPEC(filesystem_encoding, WSTR, READ_ONLY, NO_SYS),
+    SPEC(filesystem_errors, WSTR, READ_ONLY, NO_SYS),
+    SPEC(hash_seed, ULONG, READ_ONLY, NO_SYS),
+    SPEC(home, WSTR_OPT, READ_ONLY, NO_SYS),
+    SPEC(import_time, BOOL, READ_ONLY, NO_SYS),
+    SPEC(install_signal_handlers, BOOL, READ_ONLY, NO_SYS),
+    SPEC(isolated, BOOL, READ_ONLY, NO_SYS),  // sys.flags.isolated
+#ifdef MS_WINDOWS
+    SPEC(legacy_windows_stdio, BOOL, READ_ONLY, NO_SYS),
 #endif
+    SPEC(malloc_stats, BOOL, READ_ONLY, NO_SYS),
+    SPEC(orig_argv, WSTR_LIST, READ_ONLY, SYS_ATTR("orig_argv")),
+    SPEC(parse_argv, BOOL, READ_ONLY, NO_SYS),
+    SPEC(pathconfig_warnings, BOOL, READ_ONLY, NO_SYS),
+    SPEC(perf_profiling, BOOL, READ_ONLY, NO_SYS),
+    SPEC(program_name, WSTR, READ_ONLY, NO_SYS),
+    SPEC(run_command, WSTR_OPT, READ_ONLY, NO_SYS),
+    SPEC(run_filename, WSTR_OPT, READ_ONLY, NO_SYS),
+    SPEC(run_module, WSTR_OPT, READ_ONLY, NO_SYS),
 #ifdef Py_DEBUG
-    SPEC(run_presite, WSTR_OPT),
+    SPEC(run_presite, WSTR_OPT, READ_ONLY, NO_SYS),
+#endif
+    SPEC(safe_path, BOOL, READ_ONLY, NO_SYS),
+    SPEC(show_ref_count, BOOL, READ_ONLY, NO_SYS),
+    SPEC(site_import, BOOL, READ_ONLY, NO_SYS),  // sys.flags.no_site
+    SPEC(skip_source_first_line, BOOL, READ_ONLY, NO_SYS),
+    SPEC(stdio_encoding, WSTR, READ_ONLY, NO_SYS),
+    SPEC(stdio_errors, WSTR, READ_ONLY, NO_SYS),
+    SPEC(tracemalloc, UINT, READ_ONLY, NO_SYS),
+    SPEC(use_frozen_modules, BOOL, READ_ONLY, NO_SYS),
+    SPEC(use_hash_seed, BOOL, READ_ONLY, NO_SYS),
+    SPEC(user_site_directory, BOOL, READ_ONLY, NO_SYS),  // sys.flags.no_user_site
+    SPEC(warn_default_encoding, BOOL, READ_ONLY, NO_SYS),
+
+    // --- Init-only options -----------
+
+    SPEC(_config_init, UINT, INIT_ONLY, NO_SYS),
+    SPEC(_init_main, BOOL, INIT_ONLY, NO_SYS),
+    SPEC(_install_importlib, BOOL, INIT_ONLY, NO_SYS),
+    SPEC(_is_python_build, BOOL, INIT_ONLY, NO_SYS),
+    SPEC(module_search_paths_set, BOOL, INIT_ONLY, NO_SYS),
+    SPEC(pythonpath_env, WSTR_OPT, INIT_ONLY, NO_SYS),
+    SPEC(sys_path_0, WSTR_OPT, INIT_ONLY, NO_SYS),
+
+    // Array terminator
+    {NULL, 0, 0, 0, NO_SYS},
+};
+
+#undef SPEC
+#define SPEC(MEMBER, TYPE, VISIBILITY) \
+    {#MEMBER, offsetof(PyPreConfig, MEMBER), PyConfig_MEMBER_##TYPE, \
+     PyConfig_MEMBER_##VISIBILITY, NO_SYS}
+
+static const PyConfigSpec PYPRECONFIG_SPEC[] = {
+    // --- Read-only options -----------
+
+    SPEC(allocator, INT, READ_ONLY),
+    SPEC(coerce_c_locale, BOOL, READ_ONLY),
+    SPEC(coerce_c_locale_warn, BOOL, READ_ONLY),
+    SPEC(configure_locale, BOOL, READ_ONLY),
+#ifdef MS_WINDOWS
+    SPEC(legacy_windows_fs_encoding, BOOL, READ_ONLY),
 #endif
-    {NULL, 0, 0},
+    SPEC(utf8_mode, BOOL, READ_ONLY),
+
+    // --- Init-only options -----------
+    // Members already present in PYCONFIG_SPEC
+
+    SPEC(_config_init, INT, INIT_ONLY),
+    SPEC(dev_mode, BOOL, INIT_ONLY),
+    SPEC(isolated, BOOL, INIT_ONLY),
+    SPEC(parse_argv, BOOL, INIT_ONLY),
+    SPEC(use_environment, BOOL, INIT_ONLY),
+
+    // Array terminator
+    {NULL, 0, 0, 0, NO_SYS},
 };
 
 #undef SPEC
+#undef SYS_ATTR
+#undef SYS_FLAG_SETTER
+#undef SYS_FLAG
+#undef NO_SYS
+
+
+// Forward declarations
+static PyObject*
+config_get(const PyConfig *config, const PyConfigSpec *spec,
+           int use_sys);
 
 
 /* --- Command line options --------------------------------------- */
@@ -656,6 +748,28 @@ _PyWideStringList_AsList(const PyWideStringList *list)
 }
 
 
+static PyObject*
+_PyWideStringList_AsTuple(const PyWideStringList *list)
+{
+    assert(_PyWideStringList_CheckConsistency(list));
+
+    PyObject *tuple = PyTuple_New(list->length);
+    if (tuple == NULL) {
+        return NULL;
+    }
+
+    for (Py_ssize_t i = 0; i < list->length; i++) {
+        PyObject *item = PyUnicode_FromWideChar(list->items[i], -1);
+        if (item == NULL) {
+            Py_DECREF(tuple);
+            return NULL;
+        }
+        PyTuple_SET_ITEM(tuple, i, item);
+    }
+    return tuple;
+}
+
+
 /* --- Py_GetArgcArgv() ------------------------------------------- */
 
 void
@@ -1059,54 +1173,12 @@ _PyConfig_AsDict(const PyConfig *config)
 
     const PyConfigSpec *spec = PYCONFIG_SPEC;
     for (; spec->name != NULL; spec++) {
-        char *member = (char *)config + spec->offset;
-        PyObject *obj;
-        switch (spec->type) {
-        case PyConfig_MEMBER_INT:
-        case PyConfig_MEMBER_UINT:
-        {
-            int value = *(int*)member;
-            obj = PyLong_FromLong(value);
-            break;
-        }
-        case PyConfig_MEMBER_BOOL:
-        {
-            int value = *(int*)member;
-            obj = PyBool_FromLong(value);
-            break;
-        }
-        case PyConfig_MEMBER_ULONG:
-        {
-            unsigned long value = *(unsigned long*)member;
-            obj = PyLong_FromUnsignedLong(value);
-            break;
-        }
-        case PyConfig_MEMBER_WSTR:
-        case PyConfig_MEMBER_WSTR_OPT:
-        {
-            const wchar_t *wstr = *(const wchar_t**)member;
-            if (wstr != NULL) {
-                obj = PyUnicode_FromWideChar(wstr, -1);
-            }
-            else {
-                obj = Py_NewRef(Py_None);
-            }
-            break;
-        }
-        case PyConfig_MEMBER_WSTR_LIST:
-        {
-            const PyWideStringList *list = (const PyWideStringList*)member;
-            obj = _PyWideStringList_AsList(list);
-            break;
-        }
-        default:
-            Py_UNREACHABLE();
-        }
-
+        PyObject *obj = config_get(config, spec, 0);
         if (obj == NULL) {
             Py_DECREF(dict);
             return NULL;
         }
+
         int res = PyDict_SetItemString(dict, spec->name, obj);
         Py_DECREF(obj);
         if (res < 0) {
@@ -1218,15 +1290,17 @@ config_dict_get_wstrlist(PyObject *dict, const char *name, PyConfig *config,
         return -1;
     }
 
-    if (!PyList_CheckExact(list)) {
+    int is_list = PyList_CheckExact(list);
+    if (!is_list && !PyTuple_CheckExact(list)) {
         Py_DECREF(list);
         config_dict_invalid_type(name);
         return -1;
     }
 
     PyWideStringList wstrlist = _PyWideStringList_INIT;
-    for (Py_ssize_t i=0; i < PyList_GET_SIZE(list); i++) {
-        PyObject *item = PyList_GET_ITEM(list, i);
+    Py_ssize_t len = is_list ? PyList_GET_SIZE(list) : PyTuple_GET_SIZE(list);
+    for (Py_ssize_t i=0; i < len; i++) {
+        PyObject *item = is_list ? PyList_GET_ITEM(list, i) : PyTuple_GET_ITEM(list, i);
 
         if (item == Py_None) {
             config_dict_invalid_value(name);
@@ -1263,6 +1337,66 @@ error:
 }
 
 
+static int
+config_dict_get_xoptions(PyObject *dict, const char *name, PyConfig *config,
+                         PyWideStringList *result)
+{
+    PyObject *xoptions = config_dict_get(dict, name);
+    if (xoptions == NULL) {
+        return -1;
+    }
+
+    if (!PyDict_CheckExact(xoptions)) {
+        Py_DECREF(xoptions);
+        config_dict_invalid_type(name);
+        return -1;
+    }
+
+    Py_ssize_t pos = 0;
+    PyObject *key, *value;
+    PyWideStringList wstrlist = _PyWideStringList_INIT;
+    while (PyDict_Next(xoptions, &pos, &key, &value)) {
+        PyObject *item;
+
+        if (value != Py_True) {
+            item = PyUnicode_FromFormat("%S=%S", key, value);
+            if (item == NULL) {
+                goto error;
+            }
+        }
+        else {
+            item = Py_NewRef(key);
+        }
+
+        wchar_t *wstr = PyUnicode_AsWideCharString(item, NULL);
+        Py_DECREF(item);
+        if (wstr == NULL) {
+            goto error;
+        }
+
+        PyStatus status = PyWideStringList_Append(&wstrlist, wstr);
+        PyMem_Free(wstr);
+        if (_PyStatus_EXCEPTION(status)) {
+            PyErr_NoMemory();
+            goto error;
+        }
+    }
+
+    if (_PyWideStringList_Copy(result, &wstrlist) < 0) {
+        PyErr_NoMemory();
+        goto error;
+    }
+    _PyWideStringList_Clear(&wstrlist);
+    Py_DECREF(xoptions);
+    return 0;
+
+error:
+    _PyWideStringList_Clear(&wstrlist);
+    Py_DECREF(xoptions);
+    return -1;
+}
+
+
 int
 _PyConfig_FromDict(PyConfig *config, PyObject *dict)
 {
@@ -1324,9 +1458,17 @@ _PyConfig_FromDict(PyConfig *config, PyObject *dict)
         }
         case PyConfig_MEMBER_WSTR_LIST:
         {
-            if (config_dict_get_wstrlist(dict, spec->name, config,
-                                         (PyWideStringList*)member) < 0) {
-                return -1;
+            if (strcmp(spec->name, "xoptions") == 0) {
+                if (config_dict_get_xoptions(dict, spec->name, config,
+                                             (PyWideStringList*)member) < 0) {
+                    return -1;
+                }
+            }
+            else {
+                if (config_dict_get_wstrlist(dict, spec->name, config,
+                                             (PyWideStringList*)member) < 0) {
+                    return -1;
+                }
             }
             break;
         }
@@ -3261,3 +3403,505 @@ _Py_DumpPathConfig(PyThreadState *tstate)
 
     _PyErr_SetRaisedException(tstate, exc);
 }
+
+
+// --- PyConfig_Get() -------------------------------------------------------
+
+static void*
+config_spec_get_member(const PyConfigSpec *spec, const PyConfig *config)
+{
+    return (char *)config + spec->offset;
+}
+
+
+static const PyConfigSpec*
+config_generic_find_spec(const PyConfigSpec *spec, const char *name)
+{
+    for (; spec->name != NULL; spec++) {
+        if (spec->visibility == PyConfig_MEMBER_INIT_ONLY) {
+            continue;
+        }
+        if (strcmp(name, spec->name) == 0) {
+            return spec;
+        }
+    }
+    return NULL;
+}
+
+
+static const PyConfigSpec*
+config_find_spec(const char *name)
+{
+    return config_generic_find_spec(PYCONFIG_SPEC, name);
+}
+
+
+static const PyConfigSpec*
+preconfig_find_spec(const char *name)
+{
+    return config_generic_find_spec(PYPRECONFIG_SPEC, name);
+}
+
+
+static int
+config_add_xoption(PyObject *dict, const wchar_t *str)
+{
+    PyObject *name = NULL, *value = NULL;
+
+    const wchar_t *name_end = wcschr(str, L'=');
+    if (!name_end) {
+        name = PyUnicode_FromWideChar(str, -1);
+        if (name == NULL) {
+            goto error;
+        }
+        value = Py_NewRef(Py_True);
+    }
+    else {
+        name = PyUnicode_FromWideChar(str, name_end - str);
+        if (name == NULL) {
+            goto error;
+        }
+        value = PyUnicode_FromWideChar(name_end + 1, -1);
+        if (value == NULL) {
+            goto error;
+        }
+    }
+    if (PyDict_SetItem(dict, name, value) < 0) {
+        goto error;
+    }
+    Py_DECREF(name);
+    Py_DECREF(value);
+    return 0;
+
+error:
+    Py_XDECREF(name);
+    Py_XDECREF(value);
+    return -1;
+}
+
+
+PyObject*
+_PyConfig_CreateXOptionsDict(const PyConfig *config)
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return NULL;
+    }
+
+    Py_ssize_t nxoption = config->xoptions.length;
+    wchar_t **xoptions = config->xoptions.items;
+    for (Py_ssize_t i=0; i < nxoption; i++) {
+        const wchar_t *option = xoptions[i];
+        if (config_add_xoption(dict, option) < 0) {
+            Py_DECREF(dict);
+            return NULL;
+        }
+    }
+    return dict;
+}
+
+
+static PyObject*
+config_get_sys(const char *name)
+{
+    PyObject *value = PySys_GetObject(name);
+    if (value == NULL) {
+        PyErr_Format(PyExc_RuntimeError, "lost sys.%s", name);
+        return NULL;
+    }
+    return Py_NewRef(value);
+}
+
+
+static int
+config_get_sys_write_bytecode(const PyConfig *config, int *value)
+{
+    PyObject *attr = config_get_sys("dont_write_bytecode");
+    if (attr == NULL) {
+        return -1;
+    }
+
+    int is_true = PyObject_IsTrue(attr);
+    Py_DECREF(attr);
+    if (is_true < 0) {
+        return -1;
+    }
+    *value = (!is_true);
+    return 0;
+}
+
+
+static PyObject*
+config_get(const PyConfig *config, const PyConfigSpec *spec,
+           int use_sys)
+{
+    if (use_sys) {
+        if (spec->sys.attr != NULL) {
+            return config_get_sys(spec->sys.attr);
+        }
+
+        if (strcmp(spec->name, "write_bytecode") == 0) {
+            int value;
+            if (config_get_sys_write_bytecode(config, &value) < 0) {
+                return NULL;
+            }
+            return PyBool_FromLong(value);
+        }
+
+        if (strcmp(spec->name, "int_max_str_digits") == 0) {
+            PyInterpreterState *interp = _PyInterpreterState_GET();
+            return PyLong_FromLong(interp->long_state.max_str_digits);
+        }
+    }
+
+    void *member = config_spec_get_member(spec, config);
+    switch (spec->type) {
+    case PyConfig_MEMBER_INT:
+    case PyConfig_MEMBER_UINT:
+    {
+        int value = *(int *)member;
+        return PyLong_FromLong(value);
+    }
+
+    case PyConfig_MEMBER_BOOL:
+    {
+        int value = *(int *)member;
+        return PyBool_FromLong(value != 0);
+    }
+
+    case PyConfig_MEMBER_ULONG:
+    {
+        unsigned long value = *(unsigned long *)member;
+        return PyLong_FromUnsignedLong(value);
+    }
+
+    case PyConfig_MEMBER_WSTR:
+    case PyConfig_MEMBER_WSTR_OPT:
+    {
+        wchar_t *wstr = *(wchar_t **)member;
+        if (wstr != NULL) {
+            return PyUnicode_FromWideChar(wstr, -1);
+        }
+        else {
+            return Py_NewRef(Py_None);
+        }
+    }
+
+    case PyConfig_MEMBER_WSTR_LIST:
+    {
+        if (strcmp(spec->name, "xoptions") == 0) {
+            return _PyConfig_CreateXOptionsDict(config);
+        }
+        else {
+            const PyWideStringList *list = (const PyWideStringList *)member;
+            return _PyWideStringList_AsTuple(list);
+        }
+    }
+
+    default:
+        Py_UNREACHABLE();
+    }
+}
+
+
+static PyObject*
+preconfig_get(const PyPreConfig *preconfig, const PyConfigSpec *spec)
+{
+    // The type of all PYPRECONFIG_SPEC members is INT or BOOL.
+    assert(spec->type == PyConfig_MEMBER_INT
+           || spec->type == PyConfig_MEMBER_BOOL);
+
+    char *member = (char *)preconfig + spec->offset;
+    int value = *(int *)member;
+
+    if (spec->type == PyConfig_MEMBER_BOOL) {
+        return PyBool_FromLong(value != 0);
+    }
+    else {
+        return PyLong_FromLong(value);
+    }
+}
+
+
+static void
+config_unknown_name_error(const char *name)
+{
+    PyErr_Format(PyExc_ValueError, "unknown config option name: %s", name);
+}
+
+
+PyObject*
+PyConfig_Get(const char *name)
+{
+    const PyConfigSpec *spec = config_find_spec(name);
+    if (spec != NULL) {
+        const PyConfig *config = _Py_GetConfig();
+        return config_get(config, spec, 1);
+    }
+
+    spec = preconfig_find_spec(name);
+    if (spec != NULL) {
+        const PyPreConfig *preconfig = &_PyRuntime.preconfig;
+        return preconfig_get(preconfig, spec);
+    }
+
+    config_unknown_name_error(name);
+    return NULL;
+}
+
+
+int
+PyConfig_GetInt(const char *name, int *value)
+{
+    assert(!PyErr_Occurred());
+
+    PyObject *obj = PyConfig_Get(name);
+    if (obj == NULL) {
+        return -1;
+    }
+
+    if (!PyLong_Check(obj)) {
+        Py_DECREF(obj);
+        PyErr_Format(PyExc_TypeError, "config option %s is not an int", name);
+        return -1;
+    }
+
+    int as_int = PyLong_AsInt(obj);
+    Py_DECREF(obj);
+    if (as_int == -1 && PyErr_Occurred()) {
+        PyErr_Format(PyExc_OverflowError,
+                     "config option %s value does not fit into a C int", name);
+        return -1;
+    }
+
+    *value = as_int;
+    return 0;
+}
+
+
+static int
+config_names_add(PyObject *names, const PyConfigSpec *spec)
+{
+    for (; spec->name != NULL; spec++) {
+        if (spec->visibility == PyConfig_MEMBER_INIT_ONLY) {
+            continue;
+        }
+        PyObject *name = PyUnicode_FromString(spec->name);
+        if (name == NULL) {
+            return -1;
+        }
+        int res = PyList_Append(names, name);
+        Py_DECREF(name);
+        if (res < 0) {
+            return -1;
+        }
+    }
+    return 0;
+}
+
+
+PyObject*
+PyConfig_Names(void)
+{
+    PyObject *names = PyList_New(0);
+    if (names == NULL) {
+        goto error;
+    }
+
+    if (config_names_add(names, PYCONFIG_SPEC) < 0) {
+        goto error;
+    }
+    if (config_names_add(names, PYPRECONFIG_SPEC) < 0) {
+        goto error;
+    }
+
+    PyObject *frozen = PyFrozenSet_New(names);
+    Py_DECREF(names);
+    return frozen;
+
+error:
+    Py_XDECREF(names);
+    return NULL;
+}
+
+
+// --- PyConfig_Set() -------------------------------------------------------
+
+static int
+config_set_sys_flag(const PyConfigSpec *spec, int int_value)
+{
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    PyConfig *config = &interp->config;
+
+    if (spec->type == PyConfig_MEMBER_BOOL) {
+        if (int_value != 0) {
+            // convert values < 0 and values > 1 to 1
+            int_value = 1;
+        }
+    }
+
+    PyObject *value;
+    if (spec->sys.flag_setter) {
+        value = spec->sys.flag_setter(int_value);
+    }
+    else {
+        value = config_sys_flag_long(int_value);
+    }
+    if (value == NULL) {
+        return -1;
+    }
+
+    // Set sys.flags.FLAG
+    Py_ssize_t pos = spec->sys.flag_index;
+    if (_PySys_SetFlagObj(pos, value) < 0) {
+        goto error;
+    }
+
+    // Set PyConfig.ATTR
+    assert(spec->type == PyConfig_MEMBER_INT
+           || spec->type == PyConfig_MEMBER_UINT
+           || spec->type == PyConfig_MEMBER_BOOL);
+    int *member = config_spec_get_member(spec, config);
+    *member = int_value;
+
+    // Set sys.dont_write_bytecode attribute
+    if (strcmp(spec->name, "write_bytecode") == 0) {
+        if (PySys_SetObject("dont_write_bytecode", value) < 0) {
+            goto error;
+        }
+    }
+
+    Py_DECREF(value);
+    return 0;
+
+error:
+    Py_DECREF(value);
+    return -1;
+}
+
+
+int
+PyConfig_Set(const char *name, PyObject *value)
+{
+    const PyConfigSpec *spec = config_find_spec(name);
+    if (spec == NULL) {
+        spec = preconfig_find_spec(name);
+        if (spec == NULL) {
+            config_unknown_name_error(name);
+            return -1;
+        }
+        assert(spec->visibility != PyConfig_MEMBER_PUBLIC);
+    }
+
+    if (spec->visibility != PyConfig_MEMBER_PUBLIC) {
+        PyErr_Format(PyExc_ValueError, "cannot set read-only option %s",
+                     name);
+        return -1;
+    }
+
+    int int_value = 0;
+    int has_int_value = 0;
+
+    switch (spec->type) {
+    case PyConfig_MEMBER_INT:
+    case PyConfig_MEMBER_UINT:
+    case PyConfig_MEMBER_BOOL:
+        if (!PyLong_Check(value)) {
+            PyErr_Format(PyExc_TypeError, "expected int or bool, got %T", value);
+            return -1;
+        }
+        int_value = PyLong_AsInt(value);
+        if (int_value == -1 && PyErr_Occurred()) {
+            return -1;
+        }
+        if (int_value < 0 && spec->type != PyConfig_MEMBER_INT) {
+            PyErr_Format(PyExc_ValueError, "value must be >= 0");
+            return -1;
+        }
+        has_int_value = 1;
+        break;
+
+    case PyConfig_MEMBER_ULONG:
+        // not implemented: only hash_seed uses this type, and it's read-only
+        goto cannot_set;
+
+    case PyConfig_MEMBER_WSTR:
+        if (!PyUnicode_CheckExact(value)) {
+            PyErr_Format(PyExc_TypeError, "expected str, got %T", value);
+            return -1;
+        }
+        break;
+
+    case PyConfig_MEMBER_WSTR_OPT:
+        if (value != Py_None && !PyUnicode_CheckExact(value)) {
+            PyErr_Format(PyExc_TypeError, "expected str or None, got %T", value);
+            return -1;
+        }
+        break;
+
+    case PyConfig_MEMBER_WSTR_LIST:
+        if (strcmp(spec->name, "xoptions") != 0) {
+            if (!PyList_Check(value)) {
+                PyErr_Format(PyExc_TypeError, "expected list[str], got %T",
+                             value);
+                return -1;
+            }
+            for (Py_ssize_t i=0; i < PyList_GET_SIZE(value); i++) {
+                PyObject *item = PyList_GET_ITEM(value, i);
+                if (!PyUnicode_Check(item)) {
+                    PyErr_Format(PyExc_TypeError,
+                                 "expected str, list item %zd has type %T",
+                                 i, item);
+                    return -1;
+                }
+            }
+        }
+        else {
+            // xoptions type is dict[str, str]
+            if (!PyDict_Check(value)) {
+                PyErr_Format(PyExc_TypeError,
+                             "expected dict[str, str | bool], got %T",
+                             value);
+                return -1;
+            }
+
+            Py_ssize_t pos = 0;
+            PyObject *key, *item;
+            while (PyDict_Next(value, &pos, &key, &item)) {
+                if (!PyUnicode_Check(key)) {
+                    PyErr_Format(PyExc_TypeError,
+                                 "expected str, "
+                                 "got dict key type %T", key);
+                    return -1;
+                }
+                if (!PyUnicode_Check(item) && !PyBool_Check(item)) {
+                    PyErr_Format(PyExc_TypeError,
+                                 "expected str or bool, "
+                                 "got dict value type %T", key);
+                    return -1;
+                }
+            }
+        }
+        break;
+
+    default:
+        Py_UNREACHABLE();
+    }
+
+
+    if (spec->sys.attr != NULL) {
+        // Set the sys attribute, but don't set PyInterpreterState.config
+        // to keep the code simple.
+        return PySys_SetObject(spec->sys.attr, value);
+    }
+    else if (spec->sys.flag_index >= 0 && has_int_value) {
+        return config_set_sys_flag(spec, int_value);
+    }
+    else if (strcmp(spec->name, "int_max_str_digits") == 0 && has_int_value) {
+        return _PySys_SetIntMaxStrDigits(int_value);
+    }
+
+cannot_set:
+    PyErr_Format(PyExc_ValueError, "cannot set option %s", name);
+    return -1;
+}
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 1fff7e4..887a916 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -1845,6 +1845,7 @@ sys_get_int_max_str_digits_impl(PyObject *module)
     return PyLong_FromLong(interp->long_state.max_str_digits);
 }
 
+
 /*[clinic input]
 sys.set_int_max_str_digits
 
@@ -1857,16 +1858,10 @@ static PyObject *
 sys_set_int_max_str_digits_impl(PyObject *module, int maxdigits)
 /*[clinic end generated code: output=734d4c2511f2a56d input=d7e3f325db6910c5]*/
 {
-    PyThreadState *tstate = _PyThreadState_GET();
-    if ((!maxdigits) || (maxdigits >= _PY_LONG_MAX_STR_DIGITS_THRESHOLD)) {
-        tstate->interp->long_state.max_str_digits = maxdigits;
-        Py_RETURN_NONE;
-    } else {
-        PyErr_Format(
-            PyExc_ValueError, "maxdigits must be 0 or larger than %d",
-            _PY_LONG_MAX_STR_DIGITS_THRESHOLD);
+    if (_PySys_SetIntMaxStrDigits(maxdigits) < 0) {
         return NULL;
     }
+    Py_RETURN_NONE;
 }
 
 size_t
@@ -3120,6 +3115,8 @@ static PyStructSequence_Field flags_fields[] = {
     {0}
 };
 
+#define SYS_FLAGS_INT_MAX_STR_DIGITS 17
+
 static PyStructSequence_Desc flags_desc = {
     "sys.flags",        /* name */
     flags__doc__,       /* doc */
@@ -3127,6 +3124,48 @@ static PyStructSequence_Desc flags_desc = {
     18
 };
 
+static void
+sys_set_flag(PyObject *flags, Py_ssize_t pos, PyObject *value)
+{
+    assert(pos >= 0 && pos < (Py_ssize_t)(Py_ARRAY_LENGTH(flags_fields) - 1));
+
+    PyObject *old_value = PyStructSequence_GET_ITEM(flags, pos);
+    PyStructSequence_SET_ITEM(flags, pos, Py_NewRef(value));
+    Py_XDECREF(old_value);
+}
+
+
+int
+_PySys_SetFlagObj(Py_ssize_t pos, PyObject *value)
+{
+    PyObject *flags = Py_XNewRef(PySys_GetObject("flags"));
+    if (flags == NULL) {
+        if (!PyErr_Occurred()) {
+            PyErr_SetString(PyExc_RuntimeError, "lost sys.flags");
+        }
+        return -1;
+    }
+
+    sys_set_flag(flags, pos, value);
+    Py_DECREF(flags);
+    return 0;
+}
+
+
+static int
+_PySys_SetFlagInt(Py_ssize_t pos, int value)
+{
+    PyObject *obj = PyLong_FromLong(value);
+    if (obj == NULL) {
+        return -1;
+    }
+
+    int res = _PySys_SetFlagObj(pos, obj);
+    Py_DECREF(obj);
+    return res;
+}
+
+
 static int
 set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
 {
@@ -3142,8 +3181,8 @@ set_flags_from_config(PyInterpreterState *interp, PyObject *flags)
         if (value == NULL) { \
             return -1; \
         } \
-        Py_XDECREF(PyStructSequence_GET_ITEM(flags, pos)); \
-        PyStructSequence_SET_ITEM(flags, pos, value); \
+        sys_set_flag(flags, pos, value); \
+        Py_DECREF(value); \
         pos++; \
     } while (0)
 #define SetFlag(expr) SetFlagObj(PyLong_FromLong(expr))
@@ -3599,64 +3638,6 @@ err_occurred:
     return _PyStatus_ERR("can't initialize sys module");
 }
 
-static int
-sys_add_xoption(PyObject *opts, const wchar_t *s)
-{
-    PyObject *name, *value = NULL;
-
-    const wchar_t *name_end = wcschr(s, L'=');
-    if (!name_end) {
-        name = PyUnicode_FromWideChar(s, -1);
-        if (name == NULL) {
-            goto error;
-        }
-        value = Py_NewRef(Py_True);
-    }
-    else {
-        name = PyUnicode_FromWideChar(s, name_end - s);
-        if (name == NULL) {
-            goto error;
-        }
-        value = PyUnicode_FromWideChar(name_end + 1, -1);
-        if (value == NULL) {
-            goto error;
-        }
-    }
-    if (PyDict_SetItem(opts, name, value) < 0) {
-        goto error;
-    }
-    Py_DECREF(name);
-    Py_DECREF(value);
-    return 0;
-
-error:
-    Py_XDECREF(name);
-    Py_XDECREF(value);
-    return -1;
-}
-
-
-static PyObject*
-sys_create_xoptions_dict(const PyConfig *config)
-{
-    Py_ssize_t nxoption = config->xoptions.length;
-    wchar_t * const * xoptions = config->xoptions.items;
-    PyObject *dict = PyDict_New();
-    if (dict == NULL) {
-        return NULL;
-    }
-
-    for (Py_ssize_t i=0; i < nxoption; i++) {
-        const wchar_t *option = xoptions[i];
-        if (sys_add_xoption(dict, option) < 0) {
-            Py_DECREF(dict);
-            return NULL;
-        }
-    }
-
-    return dict;
-}
-
 
 // Update sys attributes for a new PyConfig configuration.
 // This function also adds attributes that _PySys_InitCore() didn't add.
@@ -3703,7 +3684,7 @@ _PySys_UpdateConfig(PyThreadState *tstate)
     COPY_LIST("orig_argv", config->orig_argv);
     COPY_LIST("warnoptions", config->warnoptions);
 
-    SET_SYS("_xoptions", sys_create_xoptions_dict(config));
+    SET_SYS("_xoptions", _PyConfig_CreateXOptionsDict(config));
 
     const wchar_t *stdlibdir = _Py_GetStdlibDir();
     if (stdlibdir != NULL) {
@@ -4129,3 +4110,28 @@ PySys_FormatStderr(const char *format, ...)
     sys_format(&_Py_ID(stderr), stderr, format, va);
     va_end(va);
 }
+
+
+int
+_PySys_SetIntMaxStrDigits(int maxdigits)
+{
+    if (maxdigits != 0 && maxdigits < _PY_LONG_MAX_STR_DIGITS_THRESHOLD) {
+        PyErr_Format(
+            PyExc_ValueError, "maxdigits must be 0 or larger than %d",
+            _PY_LONG_MAX_STR_DIGITS_THRESHOLD);
+        return -1;
+    }
+
+    // Set sys.flags.int_max_str_digits
+    const Py_ssize_t pos = SYS_FLAGS_INT_MAX_STR_DIGITS;
+    if (_PySys_SetFlagInt(pos, maxdigits) < 0) {
+        return -1;
+    }
+
+    // Set PyInterpreterState.long_state.max_str_digits
+    // and PyInterpreterState.config.int_max_str_digits.
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    interp->long_state.max_str_digits = maxdigits;
+    interp->config.int_max_str_digits = maxdigits;
+    return 0;
+}