写出一个代码，使得K1--K4控制D1、D2；K1按下D1亮、K2按下D1灭；K3按下D2亮、K4按下D2灭.

这是一个基本的开关电路控制逻辑，我们可以用Python编写一个模拟程序，这里假设`K1`到`K4`和`D1`, `D2`都作为输入和输出设备，并且它们之间的关系已经通过某种方式映射到了数字IO上。例如，在Python中可以使用`Mock`库来模拟这两个部分的交互，实际操作取决于具体的硬件环境。下面是一个简单的模拟代码：

from unittest.mock import MagicMock

class KeypadSimulator:
    def __init__(self):
        self.k1_k2 = MagicMock()
        self.k3_k4 = MagicMock()

    def press_key(self, key, state):
        if key == 'K1':
            self.k1_k2(key, state)
        elif key == 'K2':
            self.k1_k2(key, not state)
        elif key == 'K3':
            self.k3_k4(key, state)
        else:  # K4
            self.k3_k4(key, not state)

    def control_digital_outputs(self):
        if self.k1_k2.call_args[0][1]:  # K1 pressed
            self.digital_output('D1', True)
        else:
            self.digital_output('D1', False)

        if self.k3_k4.call_args[0][1]:  # K3 pressed
            self.digital_output('D2', True)
        else:
            self.digital_output('D2', False)

    def digital_output(self, pin, state):
        print(f"{pin} is {'on' if state else 'off'} when {self.k1_k2.call_args_list[-1][0][0]} is pressed.")

keypad = KeypadSimulator()
keypad.press_key('K1', True)  # Simulate pressing K1
keypad.control_digital_outputs()
keypad.press_key('K2', False)  # Simulate releasing K1
keypad.press_key('K3', True)  # Simulate pressing K3
keypad.press_key('K4', False)  # Simulate releasing K3
keypad.control_digital_outputs()

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