py/objlist: Make list += accept all arguments and add test.

py/objlist.c

@@ -121,9 +121,6 @@ STATIC mp_obj_t list_binary_op(mp_uint_t op, mp_obj_t lhs, mp_obj_t rhs) {
             return MP_OBJ_UNCAST(s);
         }
         case MP_BINARY_OP_INPLACE_ADD: {
-            if (!MP_OBJ_IS_TYPE(rhs, &mp_type_list)) {
-                return MP_OBJ_NULL; // op not supported
-            }
             list_extend(lhs, rhs);
             return lhs;
         }

tests/basics/list_extend.py

+# test list.__iadd__ and list.extend (they are equivalent)
+
+l = [1, 2]
+l.extend([])
+print(l)
+
+l.extend([3])
+print(l)
+
+l.extend([4, 5])
+print(l)
+
+l.extend(range(6, 10))
+print(l)
+
+l.extend("abc")
+print(l)
+
+l = [1, 2]
+l += []
+print(l)
+
+l += [3]
+print(l)
+
+l += [4, 5]
+print(l)
+
+l += range(6, 10)
+print(l)
+
+l += "abc"
+print(l)