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 <[email protected]>

Author: vstinner

Doc/c-api/init_config.rst

@@ -1605,6 +1605,75 @@ customized Python always running in isolated mode using
 :c:func:`Py_RunMain`.
 
 
+Runtime Python configuration API
+================================
+
+The configuration option *name* parameter must be a non-NULL null-terminated
+UTF-8 encoded string.
+
+Some options are read from the :mod:`sys` attributes. For example, the option
+``"argv"`` is read from :data:`sys.argv`.
+
+
+.. c:function:: PyObject* PyConfig_Get(const char *name)
+
+   Get the current runtime value of 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:
+
+   * ``bool``
+   * ``int``
+   * ``str``
+   * ``list[str]``
+   * ``dict[str, str]``
+
+   The caller must hold the GIL. The function cannot be called before
+   Python initialization nor after Python finalization.
+
+   .. versionadded:: 3.14
+
+
+.. c:function:: int PyConfig_GetInt(const char *name, int *value)
+
+   Similar to :c:func:`PyConfig_Get`, but get the value as a C int.
+
+   * Return ``0`` on success.
+   * Set an exception and return ``-1`` on error.
+
+   .. versionadded:: 3.14
+
+
+.. c:function:: PyObject* PyConfig_Names(void)
+
+   Get all configuration option names as a ``frozenset``.
+
+   * Return a new reference on success.
+   * Set an exception and return ``NULL`` on error.
+
+   The caller must hold the GIL. The function cannot be called before
+   Python initialization nor after Python finalization.
+
+   .. versionadded:: 3.14
+
+
+.. c:function:: int PyConfig_Set(const char *name, PyObject *value)
+
+   Set the current runtime value of a configuration option.
+
+   * Raise a :exc:`ValueError` if there is no option *name*.
+   * Raise a :exc:`ValueError` if *value* is an invalid value.
+   * Raise a :exc:`ValueError` if the option is read-only (cannot be set).
+   * Raise a :exc:`TypeError` if *value* has not the proper type.
+
+   The caller must hold the GIL. The function cannot be called before
+   Python initialization nor after Python finalization.
+
+   .. versionadded:: 3.14
+
+
 Py_GetArgcArgv()
 ================
 

Doc/whatsnew/3.14.rst

@@ -492,6 +492,15 @@ New Features
 * Add :c:func:`Py_HashBuffer` to compute and return the hash value of a buffer.
   (Contributed by Antoine Pitrou and Victor Stinner in :gh:`122854`.)
 
+* Add functions to get and set the current runtime Python configuration:
+
+  * :c:func:`PyConfig_Get`
+  * :c:func:`PyConfig_GetInt`
+  * :c:func:`PyConfig_Set`
+  * :c:func:`PyConfig_Names`
+
+  (Contributed by Victor Stinner in :gh:`107954`.)
+
 
 Porting to Python 3.14
 ----------------------

Include/cpython/initconfig.h

@@ -260,6 +260,14 @@ PyAPI_FUNC(PyStatus) PyConfig_SetWideStringList(PyConfig *config,
     Py_ssize_t length, wchar_t **items);
 
 
+/* --- PyConfig_Get() ----------------------------------------- */
+
+PyAPI_FUNC(PyObject*) PyConfig_Get(const char *name);
+PyAPI_FUNC(int) PyConfig_GetInt(const char *name, int *value);
+PyAPI_FUNC(PyObject*) PyConfig_Names(void);
+PyAPI_FUNC(int) PyConfig_Set(const char *name, PyObject *value);
+
+
 /* --- Helper functions --------------------------------------- */
 
 /* Get the original command line arguments, before Python modified them.

Include/internal/pycore_initconfig.h

@@ -181,7 +181,7 @@ 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);
 

Include/internal/pycore_sysmodule.h

@@ -29,6 +29,9 @@ extern int _PySys_SetAttr(PyObject *, PyObject *);
 extern int _PySys_ClearAttrString(PyInterpreterState *interp,
                                   const char *name, int verbose);
 
+extern int _PySys_SetFlagObj(Py_ssize_t pos, PyObject *new_value);
+extern int _PySys_SetIntMaxStrDigits(int maxdigits);
+
 #ifdef __cplusplus
 }
 #endif

Lib/test/_test_embed_set_config.py

@@ -137,7 +137,8 @@ def test_set_invalid(self):
             'warnoptions',
             'module_search_paths',
         ):
-            value_tests.append((key, invalid_wstrlist))
+            if key != 'xoptions':
+                value_tests.append((key, invalid_wstrlist))
             type_tests.append((key, 123))
             type_tests.append((key, "abc"))
             type_tests.append((key, [123]))
@@ -160,14 +161,14 @@ def test_set_invalid(self):
     def test_flags(self):
         bool_options = set(BOOL_OPTIONS)
         for sys_attr, key, value in (
-            ("debug", "parser_debug", 1),
-            ("inspect", "inspect", 2),
-            ("interactive", "interactive", 3),
-            ("optimize", "optimization_level", 4),
-            ("verbose", "verbose", 1),
-            ("bytes_warning", "bytes_warning", 10),
-            ("quiet", "quiet", 11),
-            ("isolated", "isolated", 12),
+            ("debug", "parser_debug", 2),
+            ("inspect", "inspect", 3),
+            ("interactive", "interactive", 4),
+            ("optimize", "optimization_level", 5),
+            ("verbose", "verbose", 6),
+            ("bytes_warning", "bytes_warning", 7),
+            ("quiet", "quiet", 8),
+            ("isolated", "isolated", 9),
         ):
             with self.subTest(sys=sys_attr, key=key, value=value):
                 self.set_config(**{key: value, 'parse_argv': 0})
@@ -228,9 +229,9 @@ def test_options(self):
         self.check(warnoptions=[])
         self.check(warnoptions=["default", "ignore"])
 
-        self.set_config(xoptions=[])
+        self.set_config(xoptions={})
         self.assertEqual(sys._xoptions, {})
-        self.set_config(xoptions=["dev", "tracemalloc=5"])
+        self.set_config(xoptions={"dev": True, "tracemalloc": "5"})
         self.assertEqual(sys._xoptions, {"dev": True, "tracemalloc": "5"})
 
     def test_pathconfig(self):