pythongh-107954: Add PyConfig_Get() function

Add PyConfig_Get() and PyConfig_GetInt() functions to get the current
Python configuration.

Author: vstinner

Doc/c-api/init_config.rst

@@ -1602,6 +1602,53 @@ customized Python always running in isolated mode using
 :c:func:`Py_RunMain`.
 
 
+Get the current Python configuration
+====================================
+
+Get a configuration option where *name* is the name of a :c:type:`PyConfig`
+member.
+
+Some options are read from the :mod:`sys` attributes. For example,
+:c:func:`PyConfig_Get("argv", &value) <PyConfig_Get>` reads :data:`sys.argv`.
+
+
+.. c:function:: int PyConfig_Get(const char *name, PyObject **value)
+
+   Get a configuration option as a Python object.
+
+   The object type depends on the configuration option. It can be:
+
+   * ``int``
+   * ``str``
+   * ``list[str]``
+   * ``dict[str, str]``
+
+   * Return ``0`` and set *\*value* to a Python list of strings on success.
+   * Raise an exception and return ``-1`` on error.
+
+
+.. c:function:: int PyConfig_GetInt(const char *name, int *value)
+
+   Similar to :c:func:`PyConfig_Get`, but get the value as a C int.
+
+
+Example
+-------
+
+Code::
+
+    int get_verbose(void)
+    {
+        int verbose;
+        if (PyConfig_GetInt("verbose", &verbose) < 0) {
+            // Silently ignore the error
+            PyErr_Clear();
+            return -1;
+        }
+        return verbose;
+    }
+
+
 Py_GetArgcArgv()
 ================
 

Doc/whatsnew/3.13.rst

@@ -1230,6 +1230,12 @@ New Features
   :exc:`KeyError` if the key missing.
   (Contributed by Stefan Behnel and Victor Stinner in :gh:`111262`.)
 
+* Add functions to get the current Python configuration:
+
+  * :c:func:`PyConfig_Get`
+  * :c:func:`PyConfig_GetInt`
+
+  (Contributed by Victor Stinner in :gh:`107954`.)
 
 Porting to Python 3.13
 ----------------------

Include/cpython/initconfig.h

@@ -257,6 +257,24 @@ PyAPI_FUNC(PyStatus) PyConfig_SetWideStringList(PyConfig *config,
     Py_ssize_t length, wchar_t **items);
 
 
+/* --- PyConfig_Get() ----------------------------------------- */
+
+// Get a configuration option as a Python object.
+// Return a new reference on success.
+// Set an exception and return NULL on error.
+//
+// The object type depends on the configuration option. It can be:
+// int, str, list[str] and dict[str, str].
+PyAPI_FUNC(PyObject*) PyConfig_Get(const char *name);
+
+// Get an integer configuration option.
+// Return 0 and set '*value' on success.
+// Raise an exception return -1 on error.
+PyAPI_FUNC(int) PyConfig_GetInt(
+    const char *name,
+    int *value);
+
+
 /* --- Helper functions --------------------------------------- */
 
 /* Get the original command line arguments, before Python modified them.

Include/internal/pycore_initconfig.h

@@ -169,7 +169,7 @@ extern PyStatus _PyConfig_Write(const PyConfig *config,
 extern PyStatus _PyConfig_SetPyArgv(
     PyConfig *config,
     const _PyArgv *args);
-
+extern PyObject* _PyConfig_CreateXOptionsDict(const PyConfig *config);
 
 extern void _Py_DumpPathConfig(PyThreadState *tstate);
 

Lib/test/test_capi/test_config.py

@@ -0,0 +1,105 @@
+"""
+Tests on PyConfig API (PEP 587).
+"""
+import os
+import sys
+import unittest
+from test import support
+try:
+    import _testcapi
+except ImportError:
+    _testcapi = None
+
+
+@unittest.skipIf(_testcapi is None, 'need _testcapi')
+class CAPITests(unittest.TestCase):
+    def check_config_get(self, get_func):
+        # write_bytecode is read from sys.dont_write_bytecode as int
+        with support.swap_attr(sys, "dont_write_bytecode", 0):
+            self.assertEqual(get_func('write_bytecode'), 1)
+        with support.swap_attr(sys, "dont_write_bytecode", "yes"):
+            self.assertEqual(get_func('write_bytecode'), 0)
+        with support.swap_attr(sys, "dont_write_bytecode", []):
+            self.assertEqual(get_func('write_bytecode'), 1)
+
+        # non-existent config option name
+        NONEXISTENT_KEY = 'NONEXISTENT_KEY'
+        err_msg = f'unknown config option name: {NONEXISTENT_KEY}'
+        with self.assertRaisesRegex(ValueError, err_msg):
+            get_func('NONEXISTENT_KEY')
+
+    def test_config_get(self):
+        config_get = _testcapi.config_get
+
+        self.check_config_get(config_get)
+
+        for name, config_type, expected in (
+            ('verbose', int, sys.flags.verbose),   # PyConfig_MEMBER_INT
+            ('isolated', int, sys.flags.isolated), # PyConfig_MEMBER_UINT
+            ('platlibdir', str, sys.platlibdir),   # PyConfig_MEMBER_WSTR
+            ('argv', list, sys.argv),              # PyConfig_MEMBER_WSTR_LIST
+            ('xoptions', dict, sys._xoptions),     # xoptions dict
+        ):
+            with self.subTest(name=name):
+                value = config_get(name)
+                self.assertEqual(type(value), config_type)
+                self.assertEqual(value, expected)
+
+        # PyConfig_MEMBER_ULONG type
+        hash_seed = config_get('hash_seed')
+        self.assertIsInstance(hash_seed, int)
+        self.assertGreaterEqual(hash_seed, 0)
+
+        # PyConfig_MEMBER_WSTR_OPT type
+        if 'PYTHONDUMPREFSFILE' not in os.environ:
+            self.assertIsNone(config_get('dump_refs_file'))
+
+        # attributes read from sys
+        value_str = "TEST_MARKER_STR"
+        value_list = ["TEST_MARKER_STRLIST"]
+        value_dict = {"x": "value", "y": True}
+        for name, sys_name, value in (
+            ("base_exec_prefix", None, value_str),
+            ("base_prefix", None, value_str),
+            ("exec_prefix", None, value_str),
+            ("executable", None, value_str),
+            ("platlibdir", None, value_str),
+            ("prefix", None, value_str),
+            ("pycache_prefix", None, value_str),
+            ("base_executable", "_base_executable", value_str),
+            ("stdlib_dir", "_stdlib_dir", value_str),
+            ("argv", None, value_list),
+            ("orig_argv", None, value_list),
+            ("warnoptions", None, value_list),
+            ("module_search_paths", "path", value_list),
+            ("xoptions", "_xoptions", value_dict),
+        ):
+            with self.subTest(name=name):
+                if sys_name is None:
+                    sys_name = name
+                with support.swap_attr(sys, sys_name, value):
+                    self.assertEqual(config_get(name), value)
+
+    def test_config_getint(self):
+        config_getint = _testcapi.config_getint
+
+        self.check_config_get(config_getint)
+
+        # PyConfig_MEMBER_INT type
+        self.assertEqual(config_getint('verbose'), sys.flags.verbose)
+
+        # PyConfig_MEMBER_UINT type
+        self.assertEqual(config_getint('isolated'), sys.flags.isolated)
+
+        # PyConfig_MEMBER_ULONG type
+        hash_seed = config_getint('hash_seed')
+        self.assertIsInstance(hash_seed, int)
+        self.assertGreaterEqual(hash_seed, 0)
+
+        # platlibdir is a str
+        with self.assertRaises(TypeError):
+            config_getint('platlibdir')
+
+
+if __name__ == "__main__":
+    unittest.main()

Misc/NEWS.d/next/C API/2023-12-01-21-13-32.gh-issue-107954.GO4oND.rst

@@ -0,0 +1,6 @@
+Add functions to get the current Python configuration:
+
+* :c:func:`PyConfig_Get`
+* :c:func:`PyConfig_GetInt`
+
+Patch by Victor Stinner.

Modules/Setup.stdlib.in

@@ -159,7 +159,7 @@
 @MODULE__XXTESTFUZZ_TRUE@_xxtestfuzz _xxtestfuzz/_xxtestfuzz.c _xxtestfuzz/fuzzer.c
 @MODULE__TESTBUFFER_TRUE@_testbuffer _testbuffer.c
 @MODULE__TESTINTERNALCAPI_TRUE@_testinternalcapi _testinternalcapi.c _testinternalcapi/test_lock.c _testinternalcapi/pytime.c _testinternalcapi/set.c _testinternalcapi/test_critical_sections.c
-@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/vectorcall_limited.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/bytearray.c _testcapi/bytes.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/pyos.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/heaptype_relative.c _testcapi/gc.c _testcapi/sys.c _testcapi/hash.c
+@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/vectorcall_limited.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/bytearray.c _testcapi/bytes.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/pyos.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/heaptype_relative.c _testcapi/gc.c _testcapi/sys.c _testcapi/hash.c _testcapi/config.c
 @MODULE__TESTCLINIC_TRUE@_testclinic _testclinic.c
 @MODULE__TESTCLINIC_LIMITED_TRUE@_testclinic_limited _testclinic_limited.c
 

Modules/_testcapi/config.c

@@ -0,0 +1,45 @@
+#include "parts.h"
+
+
+static PyObject *
+_testcapi_config_get(PyObject *module, PyObject *name_obj)
+{
+    const char *name;
+    if (PyArg_Parse(name_obj, "s", &name) < 0) {
+        return NULL;
+    }
+
+    return PyConfig_Get(name);
+}
+
+
+static PyObject *
+_testcapi_config_getint(PyObject *module, PyObject *name_obj)
+{
+    const char *name;
+    if (PyArg_Parse(name_obj, "s", &name) < 0) {
+        return NULL;
+    }
+
+    int value;
+    if (PyConfig_GetInt(name, &value) < 0) {
+        return NULL;
+    }
+    return PyLong_FromLong(value);
+}
+
+
+static PyMethodDef test_methods[] = {
+    {"config_get", _testcapi_config_get, METH_O},
+    {"config_getint", _testcapi_config_getint, METH_O},
+    {NULL}
+};
+
+int _PyTestCapi_Init_Config(PyObject *mod)
+{
+    if (PyModule_AddFunctions(mod, test_methods) < 0) {
+        return -1;
+    }
+
+    return 0;
+}

Modules/_testcapi/parts.h

@@ -62,5 +62,6 @@ int _PyTestCapi_Init_Hash(PyObject *module);
 
 int _PyTestCapi_Init_VectorcallLimited(PyObject *module);
 int _PyTestCapi_Init_HeaptypeRelative(PyObject *module);
+int _PyTestCapi_Init_Config(PyObject *mod);
 
 #endif // Py_TESTCAPI_PARTS_H

Modules/_testcapimodule.c

@@ -4005,6 +4005,9 @@ PyInit__testcapi(void)
     if (_PyTestCapi_Init_Hash(m) < 0) {
         return NULL;
     }
+    if (_PyTestCapi_Init_Config(m) < 0) {
+        return NULL;
+    }
 
     PyState_AddModule(m, &_testcapimodule);
     return m;