Address Victor's suggestion

Doc/using/cmdline.rst

@@ -550,6 +550,8 @@ Miscellaneous options
      *n* must be greater than or equal to 1.
      This option is useful for users who need to limit CPU resources of a container system.
      See also :envvar:`PYTHONCPUCOUNT`.
+     If *n* is "default", it follows default :func:`os.cpu_count` even if :envvar:`PYTHONCPUCOUNT`
+     is set.
 
 
    It also allows passing arbitrary values and retrieving them through the

Lib/test/test_cmd_line.py

@@ -906,6 +906,11 @@ def test_cpu_count(self):
         res = assert_python_ok('-X', 'cpu_count=4321', '-c', code)
         self.assertEqual(res.out.strip().decode("utf-8"), '4321')
 
+    def test_cpu_count_default(self):
+        code = "import os; print(os.cpu_count())"
+        res = assert_python_ok('-X', 'cpu_count=default', '-c', code)
+        self.assertEqual(int(res.out.strip().decode("utf-8")), os.cpu_count())
+
 
 @unittest.skipIf(interpreter_requires_environment(),
                  'Cannot run -I tests when PYTHON env vars are required.')

Python/initconfig.c

@@ -1706,6 +1706,10 @@ config_init_cpu_count(PyConfig *config)
         int cpu_count = -1;
         const wchar_t *sep = wcschr(xoption, L'=');
         if (sep) {
+            if (wcscmp(sep + 1, L"default") == 0) {
+                config->cpu_count = -1;
+                return _PyStatus_OK();
+            }
             if (config_wstr_to_int(sep + 1, &cpu_count) < 0 || cpu_count < 1) {
                 goto error;
             }