py/modsys.c: Add sys._exc_traceback.

DavidEGrayson · DavidEGrayson · commit e7a799e31c0c · 2023-04-11T17:11:36.000-07:00
This makes it easier to provide custom formatting of exception
stack traces, e.g. to make them fit on a tiny display.

This is an experimental function that exposes internal details
of MicroPython and it might change in the future.

Signed-off-by: David (Pololu) &lt;dev-david@pololu.com&gt;
diff --git a/py/modsys.c b/py/modsys.c
@@ -150,6 +150,24 @@ STATIC mp_obj_t mp_sys_print_exception(size_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_sys_print_exception_obj, 1, 2, mp_sys_print_exception);
 
+STATIC mp_obj_t mp_sys_exc_traceback(mp_obj_t exc) {
+    if (!mp_obj_is_exception_instance(exc)) {
+        mp_raise_TypeError(MP_ERROR_TEXT("not an exception"));
+    }
+    size_t n, *values;
+    mp_obj_exception_get_traceback(exc, &n, &values);
+    // Assumption: n is a multiple of 3.
+    mp_obj_t obj = mp_obj_new_list(n, NULL);
+    mp_obj_list_t *list = MP_OBJ_TO_PTR(obj);
+    for (size_t i = 0; i < list->len; i += 3) {
+        list->items[i + 0] = MP_OBJ_NEW_QSTR(values[i + 0]);       // filename
+        list->items[i + 1] = MP_OBJ_NEW_SMALL_INT(values[i + 1]);  // line
+        list->items[i + 2] = MP_OBJ_NEW_QSTR(values[i + 2]);       // block
+    }
+    return obj;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(mp_sys_exc_traceback_obj, mp_sys_exc_traceback);
+
 #if MICROPY_PY_SYS_EXC_INFO
 STATIC mp_obj_t mp_sys_exc_info(void) {
     mp_obj_t cur_exc = MP_OBJ_FROM_PTR(MP_STATE_VM(cur_exception));
@@ -277,6 +295,7 @@ STATIC const mp_rom_map_elem_t mp_module_sys_globals_table[] = {
      */
 
     { MP_ROM_QSTR(MP_QSTR_print_exception), MP_ROM_PTR(&mp_sys_print_exception_obj) },
+    { MP_ROM_QSTR(MP_QSTR__exc_traceback), MP_ROM_PTR(&mp_sys_exc_traceback_obj) },
     #if MICROPY_PY_SYS_ATEXIT
     { MP_ROM_QSTR(MP_QSTR_atexit), MP_ROM_PTR(&mp_sys_atexit_obj) },
     #endif
