Called when user types and releases a key. 
        The widget should be able to receive the focus in order to emit the event.
        Assign a 'tabindex' attribute to make it focusable.
        
        Args:
            key (str): the character value
            keycode (str): the numeric char code

def onkeyup(self, key, keycode, ctrl, shift, alt):
        """Called when user types and releases a key. 
        The widget should be able to receive the focus in order to emit the event.
        Assign a 'tabindex' attribute to make it focusable.
        
        Args:
            key (str): the character value
            keycode (str): the numeric char code
        """
        return (key, keycode, ctrl, shift, alt)