In the latest Python 3.8.0 installation when running IDLE on Windows, pressing "Alt + T" generates the following error:

    Exception in Tkinter callback
    Traceback (most recent call last):
      File "C:\Program Files\Python38\Lib\tkinter\__init__.py", line 1883, in __call__
        return self.func(*args)
      File "C:\Program Files\Python38\Lib\idlelib\multicall.py", line 176, in handler
        r = l[i](event)
    TypeError: toggle_tabs_event() missing 1 required positional argument: 'event'

Similarly, pressing "Alt + U" will generate a very similar error:

    Exception in Tkinter callback
    Traceback (most recent call last):
      File "C:\Program Files\Python38\Lib\tkinter\__init__.py", line 1883, in __call__
        return self.func(*args)
      File "C:\Program Files\Python38\Lib\idlelib\multicall.py", line 176, in handler
        r = l[i](event)
    TypeError: change_indentwidth_event() missing 1 required positional argument: 'event'