py/objstr: Make str.rsplit(None,n) raise NotImpl instead of assert(0).

py/objstr.c

@@ -578,7 +578,7 @@ STATIC mp_obj_t str_rsplit(mp_uint_t n_args, const mp_obj_t *args) {
     mp_int_t idx = splits;
 
     if (sep == mp_const_none) {
-        assert(!"TODO: rsplit(None,n) not implemented");
+        mp_not_implemented("rsplit(None,n)");
     } else {
         mp_uint_t sep_len;
         const char *sep_str = mp_obj_str_get_data(sep, &sep_len);

tests/misc/non_compliant.py

@@ -39,3 +39,9 @@ try:
     print('{a[0]}'.format(a=[1, 2]))
 except NotImplementedError:
     print('NotImplementedError')
+
+# str.rsplit(None, n) not implemented
+try:
+    'a a a'.rsplit(None, 1)
+except NotImplementedError:
+    print('NotImplementedError')

tests/misc/non_compliant.py.exp

@@ -4,3 +4,4 @@ True
 True
 TypeError, ValueError
 NotImplementedError
+NotImplementedError