gh-76785: Add PyInterpreterConfig Helpers (gh-117170)

These helpers make it easier to customize and inspect the config used to initialize interpreters.  This is especially valuable in our tests.  I found inspiration from the PyConfig API for the PyInterpreterConfig dict conversion stuff.  As part of this PR I've also added a bunch of tests.

Include/internal/pycore_pylifecycle.h

@@ -116,6 +116,22 @@ PyAPI_FUNC(char*) _Py_SetLocaleFromEnv(int category);
 // Export for special main.c string compiling with source tracebacks
 int _PyRun_SimpleStringFlagsWithName(const char *command, const char* name, PyCompilerFlags *flags);
 
+
+/* interpreter config */
+
+// Export for _testinternalcapi shared extension
+PyAPI_FUNC(int) _PyInterpreterConfig_InitFromState(
+    PyInterpreterConfig *,
+    PyInterpreterState *);
+PyAPI_FUNC(PyObject *) _PyInterpreterConfig_AsDict(PyInterpreterConfig *);
+PyAPI_FUNC(int) _PyInterpreterConfig_InitFromDict(
+    PyInterpreterConfig *,
+    PyObject *);
+PyAPI_FUNC(int) _PyInterpreterConfig_UpdateFromDict(
+    PyInterpreterConfig *,
+    PyObject *);
+
+
 #ifdef __cplusplus
 }
 #endif

Lib/test/support/__init__.py

@@ -1734,8 +1734,19 @@ def run_in_subinterp_with_config(code, *, own_gil=None, **config):
         raise unittest.SkipTest("requires _testinternalcapi")
     if own_gil is not None:
         assert 'gil' not in config, (own_gil, config)
-        config['gil'] = 2 if own_gil else 1
-    return _testinternalcapi.run_in_subinterp_with_config(code, **config)
+        config['gil'] = 'own' if own_gil else 'shared'
+    else:
+        gil = config['gil']
+        if gil == 0:
+            config['gil'] = 'default'
+        elif gil == 1:
+            config['gil'] = 'shared'
+        elif gil == 2:
+            config['gil'] = 'own'
+        else:
+            raise NotImplementedError(gil)
+    config = types.SimpleNamespace(**config)
+    return _testinternalcapi.run_in_subinterp_with_config(code, config)
 
 
 def _check_tracemalloc():

Lib/test/test_capi/test_misc.py

@@ -2204,6 +2204,257 @@ class SubinterpreterTest(unittest.TestCase):
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
 
+class InterpreterConfigTests(unittest.TestCase):
+
+    supported = {
+        'isolated': types.SimpleNamespace(
+            use_main_obmalloc=False,
+            allow_fork=False,
+            allow_exec=False,
+            allow_threads=True,
+            allow_daemon_threads=False,
+            check_multi_interp_extensions=True,
+            gil='own',
+        ),
+        'legacy': types.SimpleNamespace(
+            use_main_obmalloc=True,
+            allow_fork=True,
+            allow_exec=True,
+            allow_threads=True,
+            allow_daemon_threads=True,
+            check_multi_interp_extensions=False,
+            gil='shared',
+        ),
+        'empty': types.SimpleNamespace(
+            use_main_obmalloc=False,
+            allow_fork=False,
+            allow_exec=False,
+            allow_threads=False,
+            allow_daemon_threads=False,
+            check_multi_interp_extensions=False,
+            gil='default',
+        ),
+    }
+    gil_supported = ['default', 'shared', 'own']
+
+    def iter_all_configs(self):
+        for use_main_obmalloc in (True, False):
+            for allow_fork in (True, False):
+                for allow_exec in (True, False):
+                    for allow_threads in (True, False):
+                        for allow_daemon in (True, False):
+                            for checkext in (True, False):
+                                for gil in ('shared', 'own', 'default'):
+                                    yield types.SimpleNamespace(
+                                        use_main_obmalloc=use_main_obmalloc,
+                                        allow_fork=allow_fork,
+                                        allow_exec=allow_exec,
+                                        allow_threads=allow_threads,
+                                        allow_daemon_threads=allow_daemon,
+                                        check_multi_interp_extensions=checkext,
+                                        gil=gil,
+                                    )
+
+    def assert_ns_equal(self, ns1, ns2, msg=None):
+        # This is mostly copied from TestCase.assertDictEqual.
+        self.assertEqual(type(ns1), type(ns2))
+        if ns1 == ns2:
+            return
+
+        import difflib
+        import pprint
+        from unittest.util import _common_shorten_repr
+        standardMsg = '%s != %s' % _common_shorten_repr(ns1, ns2)
+        diff = ('\n' + '\n'.join(difflib.ndiff(
+                       pprint.pformat(vars(ns1)).splitlines(),
+                       pprint.pformat(vars(ns2)).splitlines())))
+        diff = f'namespace({diff})'
+        standardMsg = self._truncateMessage(standardMsg, diff)
+        self.fail(self._formatMessage(msg, standardMsg))
+
+    def test_predefined_config(self):
+        def check(name, expected):
+            expected = self.supported[expected]
+            args = (name,) if name else ()
+
+            config1 = _testinternalcapi.new_interp_config(*args)
+            self.assert_ns_equal(config1, expected)
+            self.assertIsNot(config1, expected)
+
+            config2 = _testinternalcapi.new_interp_config(*args)
+            self.assert_ns_equal(config2, expected)
+            self.assertIsNot(config2, expected)
+            self.assertIsNot(config2, config1)
+
+        with self.subTest('default'):
+            check(None, 'isolated')
+
+        for name in self.supported:
+            with self.subTest(name):
+                check(name, name)
+
+    def test_update_from_dict(self):
+        for name, vanilla in self.supported.items():
+            with self.subTest(f'noop ({name})'):
+                expected = vanilla
+                overrides = vars(vanilla)
+                config = _testinternalcapi.new_interp_config(name, **overrides)
+                self.assert_ns_equal(config, expected)
+
+            with self.subTest(f'change all ({name})'):
+                overrides = {k: not v for k, v in vars(vanilla).items()}
+                for gil in self.gil_supported:
+                    if vanilla.gil == gil:
+                        continue
+                    overrides['gil'] = gil
+                    expected = types.SimpleNamespace(**overrides)
+                    config = _testinternalcapi.new_interp_config(
+                                                            name, **overrides)
+                    self.assert_ns_equal(config, expected)
+
+            # Override individual fields.
+            for field, old in vars(vanilla).items():
+                if field == 'gil':
+                    values = [v for v in self.gil_supported if v != old]
+                else:
+                    values = [not old]
+                for val in values:
+                    with self.subTest(f'{name}.{field} ({old!r} -> {val!r})'):
+                        overrides = {field: val}
+                        expected = types.SimpleNamespace(
+                            **dict(vars(vanilla), **overrides),
+                        )
+                        config = _testinternalcapi.new_interp_config(
+                                                            name, **overrides)
+                        self.assert_ns_equal(config, expected)
+
+        with self.subTest('unsupported field'):
+            for name in self.supported:
+                with self.assertRaises(ValueError):
+                    _testinternalcapi.new_interp_config(name, spam=True)
+
+        # Bad values for bool fields.
+        for field, value in vars(self.supported['empty']).items():
+            if field == 'gil':
+                continue
+            assert isinstance(value, bool)
+            for value in [1, '', 'spam', 1.0, None, object()]:
+                with self.subTest(f'unsupported value ({field}={value!r})'):
+                    with self.assertRaises(TypeError):
+                        _testinternalcapi.new_interp_config(**{field: value})
+
+        # Bad values for .gil.
+        for value in [True, 1, 1.0, None, object()]:
+            with self.subTest(f'unsupported value(gil={value!r})'):
+                with self.assertRaises(TypeError):
+                    _testinternalcapi.new_interp_config(gil=value)
+        for value in ['', 'spam']:
+            with self.subTest(f'unsupported value (gil={value!r})'):
+                with self.assertRaises(ValueError):
+                    _testinternalcapi.new_interp_config(gil=value)
+
+    @requires_subinterpreters
+    def test_interp_init(self):
+        questionable = [
+            # strange
+            dict(
+                allow_fork=True,
+                allow_exec=False,
+            ),
+            dict(
+                gil='shared',
+                use_main_obmalloc=False,
+            ),
+            # risky
+            dict(
+                allow_fork=True,
+                allow_threads=True,
+            ),
+            # ought to be invalid?
+            dict(
+                allow_threads=False,
+                allow_daemon_threads=True,
+            ),
+            dict(
+                gil='own',
+                use_main_obmalloc=True,
+            ),
+        ]
+        invalid = [
+            dict(
+                use_main_obmalloc=False,
+                check_multi_interp_extensions=False
+            ),
+        ]
+        def match(config, override_cases):
+            ns = vars(config)
+            for overrides in override_cases:
+                if dict(ns, **overrides) == ns:
+                    return True
+            return False
+
+        def check(config):
+            script = 'pass'
+            rc = _testinternalcapi.run_in_subinterp_with_config(script, config)
+            self.assertEqual(rc, 0)
+
+        for config in self.iter_all_configs():
+            if config.gil == 'default':
+                continue
+            if match(config, invalid):
+                with self.subTest(f'invalid: {config}'):
+                    with self.assertRaises(RuntimeError):
+                        check(config)
+            elif match(config, questionable):
+                with self.subTest(f'questionable: {config}'):
+                    check(config)
+            else:
+                with self.subTest(f'valid: {config}'):
+                    check(config)
+
+    @requires_subinterpreters
+    def test_get_config(self):
+        @contextlib.contextmanager
+        def new_interp(config):
+            interpid = _testinternalcapi.new_interpreter(config)
+            try:
+                yield interpid
+            finally:
+                try:
+                    _interpreters.destroy(interpid)
+                except _interpreters.InterpreterNotFoundError:
+                    pass
+
+        with self.subTest('main'):
+            expected = _testinternalcapi.new_interp_config('legacy')
+            expected.gil = 'own'
+            interpid = _interpreters.get_main()
+            config = _testinternalcapi.get_interp_config(interpid)
+            self.assert_ns_equal(config, expected)
+
+        with self.subTest('isolated'):
+            expected = _testinternalcapi.new_interp_config('isolated')
+            with new_interp('isolated') as interpid:
+                config = _testinternalcapi.get_interp_config(interpid)
+            self.assert_ns_equal(config, expected)
+
+        with self.subTest('legacy'):
+            expected = _testinternalcapi.new_interp_config('legacy')
+            with new_interp('legacy') as interpid:
+                config = _testinternalcapi.get_interp_config(interpid)
+            self.assert_ns_equal(config, expected)
+
+        with self.subTest('custom'):
+            orig = _testinternalcapi.new_interp_config(
+                'empty',
+                use_main_obmalloc=True,
+                gil='shared',
+            )
+            with new_interp(orig) as interpid:
+                config = _testinternalcapi.get_interp_config(interpid)
+            self.assert_ns_equal(config, orig)
+
+
 @requires_subinterpreters
 class InterpreterIDTests(unittest.TestCase):
 

Lib/test/test_import/__init__.py

@@ -1823,15 +1823,19 @@ class SubinterpImportTests(unittest.TestCase):
             **(self.ISOLATED if isolated else self.NOT_ISOLATED),
             check_multi_interp_extensions=strict,
         )
+        gil = kwargs['gil']
+        kwargs['gil'] = 'default' if gil == 0 else (
+            'shared' if gil == 1 else 'own' if gil == 2 else gil)
         _, out, err = script_helper.assert_python_ok('-c', textwrap.dedent(f'''
             import _testinternalcapi, sys
             assert (
                 {name!r} in sys.builtin_module_names or
                 {name!r} not in sys.modules
             ), repr({name!r})
+            config = type(sys.implementation)(**{kwargs})
             ret = _testinternalcapi.run_in_subinterp_with_config(
                 {self.import_script(name, "sys.stdout.fileno()")!r},
-                **{kwargs},
+                config,
             )
             assert ret == 0, ret
             '''))
@@ -1847,12 +1851,16 @@ class SubinterpImportTests(unittest.TestCase):
             **(self.ISOLATED if isolated else self.NOT_ISOLATED),
             check_multi_interp_extensions=True,
         )
+        gil = kwargs['gil']
+        kwargs['gil'] = 'default' if gil == 0 else (
+            'shared' if gil == 1 else 'own' if gil == 2 else gil)
         _, out, err = script_helper.assert_python_ok('-c', textwrap.dedent(f'''
             import _testinternalcapi, sys
             assert {name!r} not in sys.modules, {name!r}
+            config = type(sys.implementation)(**{kwargs})
             ret = _testinternalcapi.run_in_subinterp_with_config(
                 {self.import_script(name, "sys.stdout.fileno()")!r},
-                **{kwargs},
+                config,
             )
             assert ret == 0, ret
             '''))

Makefile.pre.in

@@ -440,6 +440,7 @@ PYTHON_OBJS=	\
 		Python/import.o \
 		Python/importdl.o \
 		Python/initconfig.o \
+		Python/interpconfig.o \
 		Python/instrumentation.o \
 		Python/intrinsics.o \
 		Python/jit.o \
@@ -1687,6 +1688,10 @@ Modules/_xxinterpchannelsmodule.o: $(srcdir)/Modules/_xxinterpchannelsmodule.c $
 
 Python/crossinterp.o: $(srcdir)/Python/crossinterp.c $(srcdir)/Python/crossinterp_data_lookup.h $(srcdir)/Python/crossinterp_exceptions.h
 
+Python/initconfig.o: $(srcdir)/Python/initconfig.c $(srcdir)/Python/config_common.h
+
+Python/interpconfig.o: $(srcdir)/Python/interpconfig.c $(srcdir)/Python/config_common.h
+
 Python/dynload_shlib.o: $(srcdir)/Python/dynload_shlib.c Makefile
 	$(CC) -c $(PY_CORE_CFLAGS) \
 		-DSOABI='"$(SOABI)"' \

Modules/_testinternalcapi.c

@@ -23,10 +23,12 @@
 #include "pycore_initconfig.h"    // _Py_GetConfigsAsDict()
 #include "pycore_interp.h"        // _PyInterpreterState_GetConfigCopy()
 #include "pycore_long.h"          // _PyLong_Sign()
+#include "pycore_namespace.h"     // _PyNamespace_New()
 #include "pycore_object.h"        // _PyObject_IsFreed()
 #include "pycore_optimizer.h"     // _Py_UopsSymbol, etc.
 #include "pycore_pathconfig.h"    // _PyPathConfig_ClearGlobal()
 #include "pycore_pyerrors.h"      // _PyErr_ChainExceptions1()
+#include "pycore_pylifecycle.h"   // _PyInterpreterConfig_AsDict()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 
 #include "clinic/_testinternalcapi.c.h"
@@ -1355,83 +1357,153 @@ dict_getitem_knownhash(PyObject *self, PyObject *args)
 }
 
 
+static int
+init_named_interp_config(PyInterpreterConfig *config, const char *name)
+{
+    if (name == NULL) {
+        name = "isolated";
+    }
+
+    if (strcmp(name, "isolated") == 0) {
+        *config = (PyInterpreterConfig)_PyInterpreterConfig_INIT;
+    }
+    else if (strcmp(name, "legacy") == 0) {
+        *config = (PyInterpreterConfig)_PyInterpreterConfig_LEGACY_INIT;
+    }
+    else if (strcmp(name, "empty") == 0) {
+        *config = (PyInterpreterConfig){0};
+    }
+    else {
+        PyErr_Format(PyExc_ValueError,
+                     "unsupported config name '%s'", name);
+        return -1;
+    }
+    return 0;
+}
+
+static PyObject *
+new_interp_config(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    const char *name = NULL;
+    if (!PyArg_ParseTuple(args, "|s:new_config", &name)) {
+        return NULL;
+    }
+    PyObject *overrides = kwds;
+
+    if (name == NULL) {
+        name = "isolated";
+    }
+
+    PyInterpreterConfig config;
+    if (init_named_interp_config(&config, name) < 0) {
+        return NULL;
+    }
+
+    if (overrides != NULL && PyDict_GET_SIZE(overrides) > 0) {
+        if (_PyInterpreterConfig_UpdateFromDict(&config, overrides) < 0) {
+            return NULL;
+        }
+    }
+
+    PyObject *dict = _PyInterpreterConfig_AsDict(&config);
+    if (dict == NULL) {
+        return NULL;
+    }
+
+    PyObject *configobj = _PyNamespace_New(dict);
+    Py_DECREF(dict);
+    return configobj;
+}
+
+static PyObject *
+get_interp_config(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"id", NULL};
+    PyObject *idobj = NULL;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O:get_config", kwlist, &idobj))
+    {
+        return NULL;
+    }
+
+    PyInterpreterState *interp;
+    if (idobj == NULL) {
+        interp = PyInterpreterState_Get();
+    }
+    else {
+        interp = _PyInterpreterState_LookUpIDObject(idobj);
+        if (interp == NULL) {
+            return NULL;
+        }
+    }
+
+    PyInterpreterConfig config;
+    if (_PyInterpreterConfig_InitFromState(&config, interp) < 0) {
+        return NULL;
+    }
+    PyObject *dict = _PyInterpreterConfig_AsDict(&config);
+    if (dict == NULL) {
+        return NULL;
+    }
+
+    PyObject *configobj = _PyNamespace_New(dict);
+    Py_DECREF(dict);
+    return configobj;
+}
+
+static int
+interp_config_from_object(PyObject *configobj, PyInterpreterConfig *config)
+{
+    if (configobj == NULL || configobj == Py_None) {
+        if (init_named_interp_config(config, NULL) < 0) {
+            return -1;
+        }
+    }
+    else if (PyUnicode_Check(configobj)) {
+        if (init_named_interp_config(config, PyUnicode_AsUTF8(configobj)) < 0) {
+            return -1;
+        }
+    }
+    else {
+        PyObject *dict = PyObject_GetAttrString(configobj, "__dict__");
+        if (dict == NULL) {
+            PyErr_Format(PyExc_TypeError, "bad config %R", configobj);
+            return -1;
+        }
+        int res = _PyInterpreterConfig_InitFromDict(config, dict);
+        Py_DECREF(dict);
+        if (res < 0) {
+            return -1;
+        }
+    }
+    return 0;
+}
+
+
 /* To run some code in a sub-interpreter. */
 static PyObject *
 run_in_subinterp_with_config(PyObject *self, PyObject *args, PyObject *kwargs)
 {
     const char *code;
-    int use_main_obmalloc = -1;
-    int allow_fork = -1;
-    int allow_exec = -1;
-    int allow_threads = -1;
-    int allow_daemon_threads = -1;
-    int check_multi_interp_extensions = -1;
-    int gil = -1;
-    int r;
-    PyThreadState *substate, *mainstate;
-    /* only initialise 'cflags.cf_flags' to test backwards compatibility */
-    PyCompilerFlags cflags = {0};
-
-    static char *kwlist[] = {"code",
-                             "use_main_obmalloc",
-                             "allow_fork",
-                             "allow_exec",
-                             "allow_threads",
-                             "allow_daemon_threads",
-                             "check_multi_interp_extensions",
-                             "gil",
-                             NULL};
+    PyObject *configobj;
+    static char *kwlist[] = {"code", "config", NULL};
     if (!PyArg_ParseTupleAndKeywords(args, kwargs,
-                    "s$ppppppi:run_in_subinterp_with_config", kwlist,
-                    &code, &use_main_obmalloc,
-                    &allow_fork, &allow_exec,
-                    &allow_threads, &allow_daemon_threads,
-                    &check_multi_interp_extensions,
-                    &gil)) {
-        return NULL;
-    }
-    if (use_main_obmalloc < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing use_main_obmalloc");
-        return NULL;
-    }
-    if (allow_fork < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing allow_fork");
-        return NULL;
-    }
-    if (allow_exec < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing allow_exec");
-        return NULL;
-    }
-    if (allow_threads < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing allow_threads");
-        return NULL;
-    }
-    if (gil < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing gil");
-        return NULL;
-    }
-    if (allow_daemon_threads < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing allow_daemon_threads");
-        return NULL;
-    }
-    if (check_multi_interp_extensions < 0) {
-        PyErr_SetString(PyExc_ValueError, "missing check_multi_interp_extensions");
+                    "sO:run_in_subinterp_with_config", kwlist,
+                    &code, &configobj))
+    {
         return NULL;
     }
 
-    mainstate = PyThreadState_Get();
+    PyInterpreterConfig config;
+    if (interp_config_from_object(configobj, &config) < 0) {
+        return NULL;
+    }
+
+    PyThreadState *mainstate = PyThreadState_Get();
 
     PyThreadState_Swap(NULL);
 
-    const PyInterpreterConfig config = {
-        .use_main_obmalloc = use_main_obmalloc,
-        .allow_fork = allow_fork,
-        .allow_exec = allow_exec,
-        .allow_threads = allow_threads,
-        .allow_daemon_threads = allow_daemon_threads,
-        .check_multi_interp_extensions = check_multi_interp_extensions,
-        .gil = gil,
-    };
+    PyThreadState *substate;
     PyStatus status = Py_NewInterpreterFromConfig(&substate, &config);
     if (PyStatus_Exception(status)) {
         /* Since no new thread state was created, there is no exception to
@@ -1445,7 +1517,9 @@ run_in_subinterp_with_config(PyObject *self, PyObject *args, PyObject *kwargs)
         return NULL;
     }
     assert(substate != NULL);
-    r = PyRun_SimpleStringFlags(code, &cflags);
+    /* only initialise 'cflags.cf_flags' to test backwards compatibility */
+    PyCompilerFlags cflags = {0};
+    int r = PyRun_SimpleStringFlags(code, &cflags);
     Py_EndInterpreter(substate);
 
     PyThreadState_Swap(mainstate);
@@ -1473,13 +1547,21 @@ unused_interpreter_id(PyObject *self, PyObject *Py_UNUSED(ignored))
 }
 
 static PyObject *
-new_interpreter(PyObject *self, PyObject *Py_UNUSED(ignored))
+new_interpreter(PyObject *self, PyObject *args)
 {
+    PyObject *configobj = NULL;
+    if (!PyArg_ParseTuple(args, "|O:new_interpreter", &configobj)) {
+        return NULL;
+    }
+
+    PyInterpreterConfig config;
+    if (interp_config_from_object(configobj, &config) < 0) {
+        return NULL;
+    }
+
     // Unlike _interpreters.create(), we do not automatically link
     // the interpreter to its refcount.
     PyThreadState *save_tstate = PyThreadState_Get();
-    const PyInterpreterConfig config = \
-            (PyInterpreterConfig)_PyInterpreterConfig_INIT;
     PyThreadState *tstate = NULL;
     PyStatus status = Py_NewInterpreterFromConfig(&tstate, &config);
     PyThreadState_Swap(save_tstate);
@@ -1846,12 +1928,16 @@ static PyMethodDef module_functions[] = {
     {"get_object_dict_values", get_object_dict_values, METH_O},
     {"hamt", new_hamt, METH_NOARGS},
     {"dict_getitem_knownhash",  dict_getitem_knownhash,          METH_VARARGS},
+    {"new_interp_config", _PyCFunction_CAST(new_interp_config),
+     METH_VARARGS | METH_KEYWORDS},
+    {"get_interp_config", _PyCFunction_CAST(get_interp_config),
+     METH_VARARGS | METH_KEYWORDS},
     {"run_in_subinterp_with_config",
      _PyCFunction_CAST(run_in_subinterp_with_config),
      METH_VARARGS | METH_KEYWORDS},
     {"normalize_interp_id", normalize_interp_id, METH_O},
     {"unused_interpreter_id", unused_interpreter_id, METH_NOARGS},
-    {"new_interpreter", new_interpreter, METH_NOARGS},
+    {"new_interpreter", new_interpreter, METH_VARARGS},
     {"interpreter_exists", interpreter_exists, METH_O},
     {"get_interpreter_refcount", get_interpreter_refcount, METH_O},
     {"link_interpreter_refcount", link_interpreter_refcount,     METH_O},

PCbuild/_freeze_module.vcxproj

@@ -222,6 +222,7 @@
     <ClCompile Include="..\Python\import.c" />
     <ClCompile Include="..\Python\importdl.c" />
     <ClCompile Include="..\Python\initconfig.c" />
+    <ClCompile Include="..\Python\interpconfig.c" />
     <ClCompile Include="..\Python\intrinsics.c" />
     <ClCompile Include="..\Python\instrumentation.c" />
     <ClCompile Include="..\Python\jit.c" />

PCbuild/_freeze_module.vcxproj.filters

@@ -229,6 +229,9 @@
     <ClCompile Include="..\Python\initconfig.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\Python\interpconfig.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="..\Python\intrinsics.c">
       <Filter>Source Files</Filter>
     </ClCompile>

PCbuild/pythoncore.vcxproj

@@ -587,6 +587,7 @@
     <ClCompile Include="..\Python\import.c" />
     <ClCompile Include="..\Python\importdl.c" />
     <ClCompile Include="..\Python\initconfig.c" />
+    <ClCompile Include="..\Python\interpconfig.c" />
     <ClCompile Include="..\Python\intrinsics.c" />
     <ClCompile Include="..\Python\instrumentation.c" />
     <ClCompile Include="..\Python\jit.c" />

PCbuild/pythoncore.vcxproj.filters

@@ -1343,6 +1343,9 @@
     <ClCompile Include="..\Python\initconfig.c">
       <Filter>Python</Filter>
     </ClCompile>
+    <ClCompile Include="..\Python\interpconfig.c">
+      <Filter>Python</Filter>
+    </ClCompile>
     <ClCompile Include="..\Python\intrinsics.c">
       <Filter>Source Files</Filter>
     </ClCompile>

Python/config_common.h

@@ -0,0 +1,36 @@
+
+static inline int
+_config_dict_get(PyObject *dict, const char *name, PyObject **p_item)
+{
+    PyObject *item;
+    if (PyDict_GetItemStringRef(dict, name, &item) < 0) {
+        return -1;
+    }
+    if (item == NULL) {
+        // We do not set an exception.
+        return -1;
+    }
+    *p_item = item;
+    return 0;
+}
+
+
+static PyObject*
+config_dict_get(PyObject *dict, const char *name)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        if (!PyErr_Occurred()) {
+            PyErr_Format(PyExc_ValueError, "missing config key: %s", name);
+        }
+        return NULL;
+    }
+    return item;
+}
+
+
+static void
+config_dict_invalid_type(const char *name)
+{
+    PyErr_Format(PyExc_TypeError, "invalid config type: %s", name);
+}

Python/initconfig.c

@@ -24,6 +24,9 @@
 #  endif
 #endif
 
+#include "config_common.h"
+
+
 /* --- PyConfig spec ---------------------------------------------- */
 
 typedef enum {
@@ -1098,21 +1101,6 @@ _PyConfig_AsDict(const PyConfig *config)
 }
 
 
-static PyObject*
-config_dict_get(PyObject *dict, const char *name)
-{
-    PyObject *item;
-    if (PyDict_GetItemStringRef(dict, name, &item) < 0) {
-        return NULL;
-    }
-    if (item == NULL) {
-        PyErr_Format(PyExc_ValueError, "missing config key: %s", name);
-        return NULL;
-    }
-    return item;
-}
-
-
 static void
 config_dict_invalid_value(const char *name)
 {
@@ -1120,13 +1108,6 @@ config_dict_invalid_value(const char *name)
 }
 
 
-static void
-config_dict_invalid_type(const char *name)
-{
-    PyErr_Format(PyExc_TypeError, "invalid config type: %s", name);
-}
-
-
 static int
 config_dict_get_int(PyObject *dict, const char *name, int *result)
 {

Python/interpconfig.c

@@ -0,0 +1,266 @@
+/* PyInterpreterConfig API */
+
+#include "Python.h"
+#include "pycore_pylifecycle.h"
+
+#include <stdbool.h>
+
+#include "config_common.h"
+
+
+static const char *
+gil_flag_to_str(int flag)
+{
+    switch (flag) {
+    case PyInterpreterConfig_DEFAULT_GIL:
+        return "default";
+    case PyInterpreterConfig_SHARED_GIL:
+        return "shared";
+    case PyInterpreterConfig_OWN_GIL:
+        return "own";
+    default:
+        PyErr_SetString(PyExc_SystemError,
+                        "invalid interpreter config 'gil' value");
+        return NULL;
+    }
+}
+
+static int
+gil_flag_from_str(const char *str, int *p_flag)
+{
+    int flag;
+    if (str == NULL) {
+        flag = PyInterpreterConfig_DEFAULT_GIL;
+    }
+    else if (strcmp(str, "default") == 0) {
+        flag = PyInterpreterConfig_DEFAULT_GIL;
+    }
+    else if (strcmp(str, "shared") == 0) {
+        flag = PyInterpreterConfig_SHARED_GIL;
+    }
+    else if (strcmp(str, "own") == 0) {
+        flag = PyInterpreterConfig_OWN_GIL;
+    }
+    else {
+        PyErr_Format(PyExc_ValueError,
+                     "unsupported interpreter config .gil value '%s'", str);
+        return -1;
+    }
+    *p_flag = flag;
+    return 0;
+}
+
+PyObject *
+_PyInterpreterConfig_AsDict(PyInterpreterConfig *config)
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return NULL;
+    }
+
+#define ADD(NAME, OBJ)                                              \
+        do {                                                        \
+            int res = PyDict_SetItemString(dict, NAME, (OBJ));      \
+            Py_DECREF(OBJ);                                         \
+            if (res < 0) {                                          \
+                goto error;                                         \
+            }                                                       \
+        } while (0)
+#define ADD_BOOL(FIELD) \
+        ADD(#FIELD, Py_NewRef(config->FIELD ? Py_True : Py_False))
+#define ADD_STR(FIELD, STR)                                         \
+        do {                                                        \
+            if (STR == NULL) {                                      \
+                goto error;                                         \
+            }                                                       \
+            PyObject *obj = PyUnicode_FromString(STR);              \
+            if (obj == NULL) {                                      \
+                goto error;                                         \
+            }                                                       \
+            ADD(#FIELD, obj);                                       \
+        } while (0)
+
+    ADD_BOOL(use_main_obmalloc);
+    ADD_BOOL(allow_fork);
+    ADD_BOOL(allow_exec);
+    ADD_BOOL(allow_threads);
+    ADD_BOOL(allow_daemon_threads);
+    ADD_BOOL(check_multi_interp_extensions);
+
+    ADD_STR(gil, gil_flag_to_str(config->gil));
+
+#undef ADD_STR
+#undef ADD_BOOL
+#undef ADD
+
+    return dict;
+
+error:
+    Py_DECREF(dict);
+    return NULL;
+}
+
+static int
+_config_dict_get_bool(PyObject *dict, const char *name, int *p_flag)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        return -1;
+    }
+    // For now we keep things strict, rather than using PyObject_IsTrue().
+    int flag = item == Py_True;
+    if (!flag && item != Py_False) {
+        Py_DECREF(item);
+        config_dict_invalid_type(name);
+        return -1;
+    }
+    Py_DECREF(item);
+    *p_flag = flag;
+    return 0;
+}
+
+static int
+_config_dict_copy_str(PyObject *dict, const char *name,
+                      char *buf, size_t bufsize)
+{
+    PyObject *item;
+    if (_config_dict_get(dict, name, &item) < 0) {
+        return -1;
+    }
+    if (!PyUnicode_Check(item)) {
+        Py_DECREF(item);
+        config_dict_invalid_type(name);
+        return -1;
+    }
+    strncpy(buf, PyUnicode_AsUTF8(item), bufsize-1);
+    buf[bufsize-1] = '\0';
+    Py_DECREF(item);
+    return 0;
+}
+
+static int
+interp_config_from_dict(PyObject *origdict, PyInterpreterConfig *config,
+                        bool missing_allowed)
+{
+    PyObject *dict = PyDict_New();
+    if (dict == NULL) {
+        return -1;
+    }
+    if (PyDict_Update(dict, origdict) < 0) {
+        goto error;
+    }
+
+#define CHECK(NAME)                                                 \
+    do {                                                            \
+        if (PyErr_Occurred()) {                                     \
+            goto error;                                             \
+        }                                                           \
+        else {                                                      \
+            if (!missing_allowed) {                                 \
+                (void)config_dict_get(dict, NAME);                  \
+                assert(PyErr_Occurred());                           \
+                goto error;                                         \
+            }                                                       \
+        }                                                           \
+    } while (0)
+#define COPY_BOOL(FIELD)                                            \
+    do {                                                            \
+        int flag;                                                   \
+        if (_config_dict_get_bool(dict, #FIELD, &flag) < 0) {       \
+            CHECK(#FIELD);                                          \
+        }                                                           \
+        else {                                                      \
+            config->FIELD = flag;                                   \
+            (void)PyDict_PopString(dict, #FIELD, NULL);             \
+        }                                                           \
+    } while (0)
+
+    COPY_BOOL(use_main_obmalloc);
+    COPY_BOOL(allow_fork);
+    COPY_BOOL(allow_exec);
+    COPY_BOOL(allow_threads);
+    COPY_BOOL(allow_daemon_threads);
+    COPY_BOOL(check_multi_interp_extensions);
+
+    // PyInterpreterConfig.gil
+    char buf[20];
+    if (_config_dict_copy_str(dict, "gil", buf, 20) < 0) {
+        CHECK("gil");
+    }
+    else {
+        int flag;
+        if (gil_flag_from_str(buf, &flag) < 0) {
+            goto error;
+        }
+        config->gil = flag;
+        (void)PyDict_PopString(dict, "gil", NULL);
+    }
+
+#undef COPY_BOOL
+#undef CHECK
+
+    Py_ssize_t unused = PyDict_GET_SIZE(dict);
+    if (unused == 1) {
+        PyErr_Format(PyExc_ValueError,
+                     "config dict has 1 extra item (%R)", dict);
+        goto error;
+    }
+    else if (unused > 0) {
+        PyErr_Format(PyExc_ValueError,
+                     "config dict has %d extra items (%R)", unused, dict);
+        goto error;
+    }
+    return 0;
+
+error:
+    Py_DECREF(dict);
+    return -1;
+}
+
+int
+_PyInterpreterConfig_InitFromDict(PyInterpreterConfig *config, PyObject *dict)
+{
+    if (!PyDict_Check(dict)) {
+        PyErr_SetString(PyExc_TypeError, "dict expected");
+        return -1;
+    }
+    if (interp_config_from_dict(dict, config, false) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+int
+_PyInterpreterConfig_UpdateFromDict(PyInterpreterConfig *config, PyObject *dict)
+{
+    if (!PyDict_Check(dict)) {
+        PyErr_SetString(PyExc_TypeError, "dict expected");
+        return -1;
+    }
+    if (interp_config_from_dict(dict, config, true) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+int
+_PyInterpreterConfig_InitFromState(PyInterpreterConfig *config,
+                                   PyInterpreterState *interp)
+{
+    // Populate the config by re-constructing the values from the interpreter.
+    *config = (PyInterpreterConfig){
+#define FLAG(flag) \
+        (interp->feature_flags & Py_RTFLAGS_ ## flag)
+        .use_main_obmalloc = FLAG(USE_MAIN_OBMALLOC),
+        .allow_fork = FLAG(FORK),
+        .allow_exec = FLAG(EXEC),
+        .allow_threads = FLAG(THREADS),
+        .allow_daemon_threads = FLAG(DAEMON_THREADS),
+        .check_multi_interp_extensions = FLAG(MULTI_INTERP_EXTENSIONS),
+#undef FLAG
+        .gil = interp->ceval.own_gil
+            ? PyInterpreterConfig_OWN_GIL
+            : PyInterpreterConfig_SHARED_GIL,
+    };
+    return 0;
+}