gh-111374: Add a new PYTHON_FROZEN_MODULES env var, equivalent of -X frozen_modules. (#111411)

Adds a new PYTHON_FROZEN_MODULES env var to correspond with -X frozen_modules.

Co-authored-by: Hugo van Kemenade <hugovk@users.noreply.github.com>

Doc/using/cmdline.rst

@@ -535,12 +535,13 @@ Miscellaneous options
      location indicators when the interpreter displays tracebacks. See also
      :envvar:`PYTHONNODEBUGRANGES`.
    * ``-X frozen_modules`` determines whether or not frozen modules are
-     ignored by the import machinery.  A value of "on" means they get
-     imported and "off" means they are ignored.  The default is "on"
+     ignored by the import machinery.  A value of ``on`` means they get
+     imported and ``off`` means they are ignored.  The default is ``on``
      if this is an installed Python (the normal case).  If it's under
-     development (running from the source tree) then the default is "off".
-     Note that the "importlib_bootstrap" and "importlib_bootstrap_external"
-     frozen modules are always used, even if this flag is set to "off".
+     development (running from the source tree) then the default is ``off``.
+     Note that the :mod:`!importlib_bootstrap` and
+     :mod:`!importlib_bootstrap_external` frozen modules are always used, even
+     if this flag is set to ``off``. See also :envvar:`PYTHON_FROZEN_MODULES`.
    * ``-X perf`` enables support for the Linux ``perf`` profiler.
      When this option is provided, the ``perf`` profiler will be able to
      report Python calls. This option is only available on some platforms and
@@ -1095,6 +1096,20 @@ conflict.
 
    .. versionadded:: 3.13
 
+.. envvar:: PYTHON_FROZEN_MODULES
+
+   If this variable is set to ``on`` or ``off``, it determines whether or not
+   frozen modules are ignored by the import machinery.  A value of ``on`` means
+   they get imported and ``off`` means they are ignored.  The default is ``on``
+   for non-debug builds (the normal case) and ``off`` for debug builds.
+   Note that the :mod:`!importlib_bootstrap` and
+   :mod:`!importlib_bootstrap_external` frozen modules are always used, even
+   if this flag is set to ``off``.
+
+   See also the :option:`-X frozen_modules <-X>` command-line option.
+
+   .. versionadded:: 3.13
+
 
 Debug-mode variables
 ~~~~~~~~~~~~~~~~~~~~

Doc/whatsnew/3.13.rst

@@ -120,6 +120,11 @@ Other Language Changes
   is rejected when the global is used in the :keyword:`else` block.
   (Contributed by Irit Katriel in :gh:`111123`.)
 
+* Added a new environment variable :envvar:`PYTHON_FROZEN_MODULES`. It
+  determines whether or not frozen modules are ignored by the import machinery,
+  equivalent of the :option:`-X frozen_modules <-X>` command-line option.
+  (Contributed by Yilei Yang in :gh:`111374`.)
+
 New Modules
 ===========
 

Lib/test/test_cmd_line.py

@@ -153,6 +153,17 @@ class CmdLineTest(unittest.TestCase):
                 res = assert_python_ok(*cmd)
                 self.assertRegex(res.out.decode('utf-8'), expected)
 
+    def test_env_var_frozen_modules(self):
+        tests = {
+            ('on', 'FrozenImporter'),
+            ('off', 'SourceFileLoader'),
+        }
+        for raw, expected in tests:
+            cmd = ['-c', 'import os; print(os.__spec__.loader, end="")']
+            with self.subTest(raw):
+                res = assert_python_ok(*cmd, PYTHON_FROZEN_MODULES=raw)
+                self.assertRegex(res.out.decode('utf-8'), expected)
+
     def test_run_module(self):
         # Test expected operation of the '-m' switch
         # Switch needs an argument

Misc/NEWS.d/next/Core and Builtins/2023-10-27-11-22-09.gh-issue-111374.e9lrPZ.rst

@@ -0,0 +1,3 @@
+Added a new environment variable :envvar:`PYTHON_FROZEN_MODULES`. It
+determines whether or not frozen modules are ignored by the import machinery,
+equivalent of the :option:`-X frozen_modules <-X>` command-line option.

Python/initconfig.c

@@ -285,11 +285,14 @@ static const char usage_envvars[] =
 "PYTHONDEVMODE: enable the development mode.\n"
 "PYTHONPYCACHEPREFIX: root directory for bytecode cache (pyc) files.\n"
 "PYTHONWARNDEFAULTENCODING: enable opt-in EncodingWarning for 'encoding=None'.\n"
-"PYTHONNODEBUGRANGES: If this variable is set, it disables the inclusion of the \n"
+"PYTHONNODEBUGRANGES: if this variable is set, it disables the inclusion of the \n"
 "   tables mapping extra location information (end line, start column offset \n"
 "   and end column offset) to every instruction in code objects. This is useful \n"
 "   when smaller code objects and pyc files are desired as well as suppressing the \n"
 "   extra visual location indicators when the interpreter displays tracebacks.\n"
+"PYTHON_FROZEN_MODULES   : if this variable is set, it determines whether or not \n"
+"   frozen modules should be used. The default is \"on\" (or \"off\" if you are \n"
+"   running a local build).\n"
 "These variables have equivalent command-line parameters (see --help for details):\n"
 "PYTHONDEBUG             : enable parser debug mode (-d)\n"
 "PYTHONDONTWRITEBYTECODE : don't write .pyc files (-B)\n"
@@ -2132,6 +2135,19 @@ config_init_import(PyConfig *config, int compute_path_config)
         return status;
     }
 
+    const char *env = config_get_env(config, "PYTHON_FROZEN_MODULES");
+    if (env == NULL) {
+    }
+    else if (strcmp(env, "on") == 0) {
+        config->use_frozen_modules = 1;
+    }
+    else if (strcmp(env, "off") == 0) {
+        config->use_frozen_modules = 0;
+    } else {
+        return PyStatus_Error("bad value for PYTHON_FROZEN_MODULES "
+                              "(expected \"on\" or \"off\")");
+    }
+
     /* -X frozen_modules=[on|off] */
     const wchar_t *value = config_get_xoption_value(config, L"frozen_modules");
     if (value == NULL) {