def check_presses(self):
        """
        Return the set of Buttons which have been pressed since this call was last made, clearing it as we do.

        :return:
            A ButtonPresses instance which contains buttons which were pressed since this call was last made.
        """
        pressed = []
        for button, state in self.buttons.items():
            if state.was_pressed_since_last_check:
                pressed.append(button)
                state.was_pressed_since_last_check = False
        self.__presses = ButtonPresses(pressed)
        return self.__presses