py: Add checks for stream objects in print() and sys.print_exception().

py/modbuiltins.c

@@ -386,7 +386,7 @@ STATIC mp_obj_t mp_builtin_print(size_t n_args, const mp_obj_t *pos_args, mp_map
     mp_arg_parse_all(0, NULL, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, u.args);
 
     #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
-    // TODO file may not be a concrete object (eg it could be a small-int)
+    mp_get_stream_raise(u.args[ARG_file].u_obj, MP_STREAM_OP_WRITE);
     mp_print_t print = {MP_OBJ_TO_PTR(u.args[ARG_file].u_obj), mp_stream_write_adaptor};
     #endif
 

py/modsys.c

@@ -106,7 +106,8 @@ STATIC mp_obj_t mp_sys_print_exception(size_t n_args, const mp_obj_t *args) {
     #if MICROPY_PY_IO && MICROPY_PY_SYS_STDFILES
     void *stream_obj = &mp_sys_stdout_obj;
     if (n_args > 1) {
-        stream_obj = MP_OBJ_TO_PTR(args[1]); // XXX may fail
+        mp_get_stream_raise(args[1], MP_STREAM_OP_WRITE);
+        stream_obj = MP_OBJ_TO_PTR(args[1]);
     }
 
     mp_print_t print = {stream_obj, mp_stream_write_adaptor};