bpo-38234: Complete init config documentation (GH-16404)

Doc/c-api/init_config.rst

@@ -241,6 +241,7 @@ PyPreConfig
       locale to decide if it should be coerced.
 
    .. c:member:: int coerce_c_locale_warn
+
       If non-zero, emit a warning if the C locale is coerced.
 
    .. c:member:: int dev_mode
@@ -300,7 +301,7 @@ For :ref:`Python Configuration <init-python-config>`
 (:c:func:`PyPreConfig_InitPythonConfig`), if Python is initialized with
 command line arguments, the command line arguments must also be passed to
 preinitialize Python, since they have an effect on the pre-configuration
-like encodings. For example, the :option:`-X` ``utf8`` command line option
+like encodings. For example, the :option:`-X utf8 <-X>` command line option
 enables the UTF-8 Mode.
 
 ``PyMem_SetAllocator()`` can be called after :c:func:`Py_PreInitialize` and
@@ -464,7 +465,7 @@ PyConfig
 
    .. c:member:: int dev_mode
 
-      Development mode: see :option:`-X` ``dev``.
+      Development mode: see :option:`-X dev <-X>`.
 
    .. c:member:: int dump_refs
 
@@ -482,7 +483,7 @@ PyConfig
 
    .. c:member:: int faulthandler
 
-      If non-zero, call :func:`faulthandler.enable`.
+      If non-zero, call :func:`faulthandler.enable` at startup.
 
    .. c:member:: wchar_t* filesystem_encoding
 
@@ -504,6 +505,9 @@ PyConfig
 
       Python home directory.
 
+      Initialized from :envvar:`PYTHONHOME` environment variable value by
+      default.
+
    .. c:member:: int import_time
 
       If non-zero, profile import time.
@@ -561,7 +565,7 @@ PyConfig
 
       :data:`sys.path`. If :c:member:`~PyConfig.module_search_paths_set` is
       equal to 0, the :c:member:`~PyConfig.module_search_paths` is overridden
-      by the function computing the :ref:`Path Configuration
+      by the function calculating the :ref:`Path Configuration
       <init-path-config>`.
 
    .. c:member:: int optimization_level
@@ -586,9 +590,9 @@ PyConfig
 
    .. c:member:: int pathconfig_warnings
 
-      If equal to 0, suppress warnings when computing the path configuration
-      (Unix only, Windows does not log any warning). Otherwise, warnings are
-      written into ``stderr``.
+      If equal to 0, suppress warnings when calculating the :ref:`Path
+      Configuration <init-path-config>` (Unix only, Windows does not log any
+      warning). Otherwise, warnings are written into ``stderr``.
 
    .. c:member:: wchar_t* prefix
 
@@ -596,39 +600,46 @@ PyConfig
 
    .. c:member:: wchar_t* program_name
 
-      Program name.
+      Program name. Used to initialize :c:member:`~PyConfig.executable`, and in
+      early error messages.
 
    .. c:member:: wchar_t* pycache_prefix
 
-      ``.pyc`` cache prefix.
+      :data:`sys.pycache_prefix`: ``.pyc`` cache prefix.
+
+      If NULL, :data:`sys.pycache_prefix` is set to ``None``.
 
    .. c:member:: int quiet
 
       Quiet mode. For example, don't display the copyright and version messages
-      even in interactive mode.
+      in interactive mode.
 
    .. c:member:: wchar_t* run_command
 
-      ``python3 -c COMMAND`` argument.
+      ``python3 -c COMMAND`` argument. Used by :c:func:`Py_RunMain`.
 
    .. c:member:: wchar_t* run_filename
 
-      ``python3 FILENAME`` argument.
+      ``python3 FILENAME`` argument. Used by :c:func:`Py_RunMain`.
 
    .. c:member:: wchar_t* run_module
 
-      ``python3 -m MODULE`` argument.
+      ``python3 -m MODULE`` argument. Used by :c:func:`Py_RunMain`.
 
    .. c:member:: int show_alloc_count
 
       Show allocation counts at exit?
 
+      Set to 1 by :option:`-X showalloccount <-X>` command line option.
+
       Need a special Python build with ``COUNT_ALLOCS`` macro defined.
 
    .. c:member:: int show_ref_count
 
       Show total reference count at exit?
 
+      Set to 1 by :option:`-X showrefcount <-X>` command line option.
+
       Need a debug build of Python (``Py_REF_DEBUG`` macro must be defined).
 
    .. c:member:: int site_import
@@ -647,7 +658,7 @@ PyConfig
 
    .. c:member:: int tracemalloc
 
-      If non-zero, call :func:`tracemalloc.start`.
+      If non-zero, call :func:`tracemalloc.start` at startup.
 
    .. c:member:: int use_environment
 
@@ -669,6 +680,9 @@ PyConfig
 
       If non-zero, write ``.pyc`` files.
 
+      :data:`sys.dont_write_bytecode` is initialized to the inverted value of
+      :c:member:`~PyConfig.write_bytecode`.
+
    .. c:member:: PyWideStringList xoptions
 
       :data:`sys._xoptions`.
@@ -694,8 +708,8 @@ Function to initialize Python:
 The caller is responsible to handle exceptions (error or exit) using
 :c:func:`PyStatus_Exception` and :c:func:`Py_ExitStatusException`.
 
-``PyImport_FrozenModules``, ``PyImport_AppendInittab()`` or
-``PyImport_ExtendInittab()`` is used: they must be set or called after Python
+If ``PyImport_FrozenModules``, ``PyImport_AppendInittab()`` or
+``PyImport_ExtendInittab()`` are used, they must be set or called after Python
 preinitialization and before the Python initialization.
 
 Example setting the program name::
@@ -760,7 +774,7 @@ configuration, and then override some parameters::
 
         /* Append our custom search path to sys.path */
         status = PyWideStringList_Append(&config.module_search_paths,
-                                      L"/path/to/more/modules");
+                                         L"/path/to/more/modules");
         if (PyStatus_Exception(status)) {
             goto done;
         }
@@ -791,9 +805,9 @@ isolate Python from the system. For example, to embed Python into an
 application.
 
 This configuration ignores global configuration variables, environments
-variables and command line arguments (:c:member:`PyConfig.argv` is not parsed).
-The C standard streams (ex: ``stdout``) and the LC_CTYPE locale are left
-unchanged by default.
+variables, command line arguments (:c:member:`PyConfig.argv` is not parsed)
+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
@@ -970,7 +984,7 @@ initialization, the core feature of the :pep:`432`:
   * Builtin exceptions;
   * Builtin and frozen modules;
   * The :mod:`sys` module is only partially initialized
-    (ex: :data:`sys.path` doesn't exist yet);
+    (ex: :data:`sys.path` doesn't exist yet).
 
 * "Main" initialization phase, Python is fully initialized:
 
@@ -996,9 +1010,9 @@ No module is imported during the "Core" phase and the ``importlib`` module is
 not configured: the :ref:`Path Configuration <init-path-config>` is only
 applied during the "Main" phase. It may allow to customize Python in Python to
 override or tune the :ref:`Path Configuration <init-path-config>`, maybe
-install a custom sys.meta_path importer or an import hook, etc.
+install a custom :data:`sys.meta_path` importer or an import hook, etc.
 
-It may become possible to compute the :ref:`Path Configuration
+It may become possible to calculatin the :ref:`Path Configuration
 <init-path-config>` in Python, after the Core phase and before the Main phase,
 which is one of the :pep:`432` motivation.