add two attribute to str cls that let test_string could pass

from_cpython/Objects/stringobject.c

@@ -23,6 +23,22 @@ PyObject * _do_string_format(PyObject *self, PyObject *args, PyObject *kwargs) {
     return do_string_format(self, args, kwargs);
 }
 
+void _string_init() {
+    if (PyType_Ready(&PyFieldNameIter_Type) < 0)
+        Py_FatalError("Can't initialize field name iterator type");
+
+    if (PyType_Ready(&PyFormatterIter_Type) < 0)
+        Py_FatalError("Can't initialize formatter iter type");
+}
+
+PyObject * _formatter_parser(STRINGLIB_OBJECT *self) {
+    return formatter_parser(self);
+}
+
+PyObject * _formatter_field_name_split(STRINGLIB_OBJECT *self) {
+    return formatter_field_name_split(self);
+}
+
 PyObject *
 string_count(PyStringObject *self,
              PyObject *sub_obj, PyObject* obj_start, PyObject** args)

src/runtime/str.cpp

@@ -45,6 +45,8 @@ extern "C" PyObject* string_rfind(PyStringObject* self, PyObject* args) noexcept
 extern "C" PyObject* string_replace(PyStringObject* self, PyObject* args) noexcept;
 extern "C" PyObject* string_splitlines(PyStringObject* self, PyObject* args) noexcept;
 extern "C" PyObject* string__format__(PyObject* self, PyObject* args) noexcept;
+extern "C" PyObject* _formatter_parser(PyStringObject* self) noexcept;
+extern "C" PyObject* _formatter_field_name_split(PyStringObject* self) noexcept;
 
 // from cpython's stringobject.c:
 #define LEFTSTRIP 0
@@ -2784,6 +2786,8 @@ static PyMethodDef string_methods[] = {
     { "splitlines", (PyCFunction)string_splitlines, METH_VARARGS, NULL },
     { "zfill", (PyCFunction)string_zfill, METH_VARARGS, NULL },
     { "__format__", (PyCFunction)string__format__, METH_VARARGS, NULL },
+    { "_formatter_parser", (PyCFunction)_formatter_parser, METH_NOARGS, NULL },
+    { "_formatter_field_name_split", (PyCFunction)_formatter_field_name_split, METH_NOARGS, NULL },
 };
 
 void setupStr() {

src/runtime/types.cpp

@@ -77,6 +77,7 @@ extern "C" void initzlib();
 extern "C" void init_codecs();
 extern "C" void init_socket();
 extern "C" void _PyUnicode_Init();
+extern "C" void _string_init();
 extern "C" void initunicodedata();
 extern "C" void init_weakref();
 extern "C" void initcStringIO();
@@ -3936,6 +3937,7 @@ void setupRuntime() {
     setupClassobj();
     setupSuper();
     _PyUnicode_Init();
+    _string_init();
     setupDescr();
     setupTraceback();
     setupCode();