Python中如何实现备忘录模式 设计模式在状态恢复中的作用

class Originator:
    def __init__(self, state):
        self._state = state

    def set_state(self, state):
        self._state = state
        print(f"State set to: {self._state}")

    def create_memento(self):
        print("Saving current state to Memento.")
        return Memento(self._state)

    def restore_from_memento(self, memento):
        self._state = memento.get_state()
        print(f"State restored to: {self._state}")

class Memento:
    def __init__(self, state):
        self._state = state

    def get_state(self):
        return self._state

class Caretaker:
    def __init__(self, originator):
        self._mementos = []
        self._originator = originator

    def add_memento(self, memento):
        self._mementos.append(memento)

    def get_memento(self, index):
        return self._mementos[index]

# 示例
originator = Originator("State #1")
caretaker = Caretaker(originator)

caretaker.add_memento(originator.create_memento())
originator.set_state("State #2")
caretaker.add_memento(originator.create_memento())
originator.set_state("State #3")

print("Now let's rollback to State #1")
originator.restore_from_memento(caretaker.get_memento(0))

class TextEditor:
    def __init__(self):
        self._text = ""
        self._history = []

    def write(self, text):
        self._history.append(self.create_memento())
        self._text += text
        print(f"Wrote: {text}, Current text: {self._text}")

    def undo(self):
        if self._history:
            memento = self._history.pop()
            self.restore_from_memento(memento)
            print(f"Undo, Current text: {self._text}")
        else:
            print("Nothing to undo.")

    def create_memento(self):
        return Memento(self._text)

    def restore_from_memento(self, memento):
        self._text = memento.get_state()

# 示例
editor = TextEditor()
editor.write("Hello, ")
editor.write("World!")
editor.undo()
editor.write("Python!")
editor.undo()
editor.undo()