bpo-42260: Fix _PyConfig_Read() if compute_path_config=0

Doc/c-api/init.rst

@@ -376,6 +376,12 @@ Process-wide parameters
  The returned string points into static storage; the caller should not modify its
  value.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. c:function:: wchar_t* Py_GetPrefix()
 
@@ -389,6 +395,12 @@ Process-wide parameters
  script at build time. The value is available to Python code as ``sys.prefix``.
  It is only useful on Unix. See also the next function.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. c:function:: wchar_t* Py_GetExecPrefix()
 
@@ -424,6 +436,12 @@ Process-wide parameters
  while having :file:`/usr/local/plat` be a different filesystem for each
  platform.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. c:function:: wchar_t* Py_GetProgramFullPath()
 
@@ -437,6 +455,12 @@ Process-wide parameters
  static storage; the caller should not modify its value. The value is available
  to Python code as ``sys.executable``.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. c:function:: wchar_t* Py_GetPath()
 
@@ -455,8 +479,14 @@ Process-wide parameters
  can be (and usually is) modified later to change the search path for loading
  modules.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
  .. XXX should give the exact rules
 
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. c:function:: void Py_SetPath(const wchar_t *)
 
@@ -638,6 +668,12 @@ Process-wide parameters
  :c:func:`Py_SetPythonHome`, or the value of the :envvar:`PYTHONHOME`
  environment variable if it is set.
 
+ This function should not be called before :c:func:`Py_Initialize`, otherwise
+ it returns ``NULL``.
+
+ .. versionchanged:: 3.10
+ It now returns ``NULL`` if called before :c:func:`Py_Initialize`.
+
 
 .. _threads:
 

Doc/c-api/init_config.rst

@@ -24,11 +24,15 @@ There are two kinds of configuration:
  environments variables are ignored, the LC_CTYPE locale is left unchanged and
  no signal handler is registred.
 
+The :c:func:`Py_RunMain` function can be used to write a customized Python
+program.
+
 See also :ref:`Initialization, Finalization, and Threads <initialization>`.
 
 .. seealso::
  :pep:`587` "Python Initialization Configuration".
 
+
 Example
 =======
 
@@ -532,7 +536,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: wchar_t* base_executable
 
@@ -544,15 +548,15 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: wchar_t* base_prefix
 
  :data:`sys.base_prefix`.
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: int buffered_stdio
 
@@ -634,7 +638,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: wchar_t* executable
 
@@ -643,7 +647,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: int faulthandler
 
@@ -726,7 +730,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` input.
+ Part of the :ref:`Python Path Configuration <init-path-config>` input.
 
  .. c:member:: int import_time
 
@@ -817,7 +821,7 @@ PyConfig
  Default: value of the ``PLATLIBDIR`` macro which is set at configure time
  by ``--with-platlibdir`` (default: ``"lib"``).
 
- Part of the :ref:`Path Configuration <init-path-config>` input.
+ Part of the :ref:`Python Path Configuration <init-path-config>` input.
 
  .. versionadded:: 3.9
 
@@ -830,22 +834,22 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` input.
+ Part of the :ref:`Python Path Configuration <init-path-config>` input.
 
  .. c:member:: PyWideStringList module_search_paths
  .. c:member:: int module_search_paths_set
 
  Module search paths: :data:`sys.path`.
 
  If :c:member:`~PyConfig.module_search_paths_set` is equal to 0, the
- function calculating the :ref:`Path Configuration <init-path-config>`
+ function calculating the :ref:`Python Path Configuration <init-path-config>`
  overrides the :c:member:`~PyConfig.module_search_paths` and sets
  :c:member:`~PyConfig.module_search_paths_set` to ``1``.
 
  Default: empty list (``module_search_paths``) and ``0``
  (``module_search_paths_set``).
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: int optimization_level
 
@@ -911,15 +915,15 @@ PyConfig
 
  .. c:member:: int pathconfig_warnings
 
- On Unix, if non-zero, calculating the :ref:`Path Configuration
+ On Unix, if non-zero, calculating the :ref:`Python Path Configuration
  <init-path-config>` can log warnings into ``stderr``. If equals to 0,
  suppress these warnings.
 
  It has no effect on Windows.
 
  Default: ``1`` in Python mode, ``0`` in isolated mode.
 
- Part of the :ref:`Path Configuration <init-path-config>` input.
+ Part of the :ref:`Python Path Configuration <init-path-config>` input.
 
  .. c:member:: wchar_t* prefix
 
@@ -928,7 +932,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` output.
+ Part of the :ref:`Python Path Configuration <init-path-config>` output.
 
  .. c:member:: wchar_t* program_name
 
@@ -946,7 +950,7 @@ PyConfig
 
  Default: ``NULL``.
 
- Part of the :ref:`Path Configuration <init-path-config>` input.
+ Part of the :ref:`Python Path Configuration <init-path-config>` input.
 
  .. c:member:: wchar_t* pycache_prefix
 
@@ -1262,7 +1266,7 @@ and user site directory. The C standard streams (ex: ``stdout``) and the
 LC_CTYPE locale are left unchanged. Signal handlers are not installed.
 
 Configuration files are still used with this configuration. Set the
-:ref:`Path Configuration <init-path-config>` ("output fields") to ignore these
+:ref:`Python Path Configuration <init-path-config>` ("output fields") to ignore these
 configuration files and avoid the function computing the default path
 configuration.
 
@@ -1287,8 +1291,8 @@ and :ref:`Python UTF-8 Mode <utf8-mode>`
 
 .. _init-path-config:
 
-Path Configuration
-==================
+Python Path Configuration
+=========================
 
 :c:type:`PyConfig` contains multiple fields for the path configuration:
 

Doc/whatsnew/3.10.rst

@@ -486,6 +486,14 @@ Porting to Python 3.10
  ``unicodedata.ucnhash_CAPI`` has been moved to the internal C API.
  (Contributed by Victor Stinner in :issue:`42157`.)
 
+* :c:func:`Py_GetPath`, :c:func:`Py_GetPrefix`, :c:func:`Py_GetExecPrefix`,
+ :c:func:`Py_GetProgramFullPath`, :c:func:`Py_GetPythonHome` and
+ :c:func:`Py_GetProgramName` functions now return ``NULL`` if called before
+ :c:func:`Py_Initialize` (before Python is initialized). Use the new
+ :ref:`Python Initialization Configuration API <init-config>` to get the
+ :ref:`Python Path Configuration. <init-path-config>`.
+ (Contributed by Victor Stinner in :issue:`42260`.)
+
 Deprecated
 ----------
 

Include/internal/pycore_initconfig.h

@@ -151,7 +151,9 @@ PyAPI_FUNC(void) _PyConfig_InitCompatConfig(PyConfig *config);
 extern PyStatus _PyConfig_Copy(
  PyConfig *config,
  const PyConfig *config2);
-extern PyStatus _PyConfig_InitPathConfig(PyConfig *config);
+extern PyStatus _PyConfig_InitPathConfig(
+ PyConfig *config,
+ int compute_path_config);
 extern PyStatus _PyConfig_Read(PyConfig *config, int compute_path_config);
 extern PyStatus _PyConfig_Write(const PyConfig *config,
  struct pyruntimestate *runtime);

Misc/NEWS.d/next/C API/2020-11-10-14-27-39.bpo-42260.-Br3Co.rst

@@ -0,0 +1,7 @@
+:c:func:`Py_GetPath`, :c:func:`Py_GetPrefix`, :c:func:`Py_GetExecPrefix`,
+:c:func:`Py_GetProgramFullPath`, :c:func:`Py_GetPythonHome` and
+:c:func:`Py_GetProgramName` functions now return ``NULL`` if called before
+:c:func:`Py_Initialize` (before Python is initialized). Use the new
+:ref:`Python Initialization Configuration API <init-config>` to get the
+:ref:`Python Path Configuration. <init-path-config>`. Patch by Victor
+Stinner.

Python/initconfig.c

@@ -2069,8 +2069,8 @@ config_read(PyConfig *config, int compute_path_config)
  }
  }
 
- if (compute_path_config && config->_install_importlib) {
- status = _PyConfig_InitPathConfig(config);
+ if (config->_install_importlib) {
+ status = _PyConfig_InitPathConfig(config, compute_path_config);
  if (_PyStatus_EXCEPTION(status)) {
  return status;
  }