gh-126223: Propagate unicode errors in _interpreters.create()

Lib/test/test_interpreters/test_api.py

@@ -54,6 +54,9 @@ def test_in_main(self):
         self.assertIsInstance(interp, interpreters.Interpreter)
         self.assertIn(interp, interpreters.list_all())
 
+        # GH-126221: Passing an invalid Unicode character used to cause a SystemError
+        self.assertRaises(UnicodeEncodeError, _interpreters.create, '\udc80')
+
     def test_in_thread(self):
         lock = threading.Lock()
         interp = None

Misc/NEWS.d/next/Library/2024-10-30-23-42-44.gh-issue-126223.k2qooc.rst

@@ -0,0 +1,2 @@
+Raise a :exc:`UnicodeEncodeError` instead of a :exc:`SystemError` upon
+calling :func:`!_interpreters.create` with an invalid Unicode character.

Modules/_interpretersmodule.c

@@ -402,7 +402,11 @@ config_from_object(PyObject *configobj, PyInterpreterConfig *config)
         }
     }
     else if (PyUnicode_Check(configobj)) {
-        if (init_named_config(config, PyUnicode_AsUTF8(configobj)) < 0) {
+        const char *utf8name = PyUnicode_AsUTF8(configobj);
+        if (utf8name == NULL) {
+            return -1;
+        }
+        if (init_named_config(config, utf8name) < 0) {
             return -1;
         }
     }