def _clear_ui(self):
        """Clear the canvas and set detected digit values and the calculation answer to None."""
        self._canvas[:] = 255
        self._op1, self._op1_prob = None, None
        self._op2, self._op2_prob = None, None
        self._answer = None
Clear the canvas and set detected digit values and the calculation answer to None.
apps/mnist_calc/mnist_calc.py