Pamiątka w języku Python

from __future__ import annotations from abc import ABC, abstractmethod from datetime import datetime from random import sample from string import ascii_letters class Originator: """ The Originator holds some important state that may change over time. It also defines a method for saving the state inside a memento and another method for restoring the state from it. """ _state = None """ For the sake of simplicity, the originator's state is stored inside a single variable. """ def __init__(self, state: str) -> None: self._state = state print(f"Originator: My initial state is: {self._state}") def do_something(self) -> None: """ The Originator's business logic may affect its internal state. Therefore, the client should backup the state before launching methods of the business logic via the save() method. """ print("Originator: I'm doing something important.") self._state = self._generate_random_string(30) print(f"Originator: and my state has changed to: {self._state}") @staticmethod def _generate_random_string(length: int = 10) -> str: return "".join(sample(ascii_letters, length)) def save(self) -> Memento: """ Saves the current state inside a memento. """ return ConcreteMemento(self._state) def restore(self, memento: Memento) -> None: """ Restores the Originator's state from a memento object. """ self._state = memento.get_state() print(f"Originator: My state has changed to: {self._state}") class Memento(ABC): """ The Memento interface provides a way to retrieve the memento's metadata, such as creation date or name. However, it doesn't expose the Originator's state. """ @abstractmethod def get_name(self) -> str: pass @abstractmethod def get_date(self) -> str: pass class ConcreteMemento(Memento): def __init__(self, state: str) -> None: self._state = state self._date = str(datetime.now())[:19] def get_state(self) -> str: """ The Originator uses this method when restoring its state. """ return self._state def get_name(self) -> str: """ The rest of the methods are used by the Caretaker to display metadata. """ return f"{self._date} / ({self._state[0:9]}...)" def get_date(self) -> str: return self._date class Caretaker: """ The Caretaker doesn't depend on the Concrete Memento class. Therefore, it doesn't have access to the originator's state, stored inside the memento. It works with all mementos via the base Memento interface. """ def __init__(self, originator: Originator) -> None: self._mementos = [] self._originator = originator def backup(self) -> None: print("\nCaretaker: Saving Originator's state...") self._mementos.append(self._originator.save()) def undo(self) -> None: if not len(self._mementos): return memento = self._mementos.pop() print(f"Caretaker: Restoring state to: {memento.get_name()}") try: self._originator.restore(memento) except Exception: self.undo() def show_history(self) -> None: print("Caretaker: Here's the list of mementos:") for memento in self._mementos: print(memento.get_name()) if __name__ == "__main__": originator = Originator("Super-duper-super-puper-super.") caretaker = Caretaker(originator) caretaker.backup() originator.do_something() caretaker.backup() originator.do_something() caretaker.backup() originator.do_something() print() caretaker.show_history() print("\nClient: Now, let's rollback!\n") caretaker.undo() print("\nClient: Once more!\n") caretaker.undo() 

Originator: My initial state is: Super-duper-super-puper-super. Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: wQAehHYOqVSlpEXjyIcgobrxsZUnat Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: lHxNORKcsgMWYnJqoXjVCbQLEIeiSp Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: cvIYsRilNOtwynaKdEZpDCQkFAXVMf Caretaker: Here's the list of mementos: 2019-01-26 21:11:24 / (Super-dup...) 2019-01-26 21:11:24 / (wQAehHYOq...) 2019-01-26 21:11:24 / (lHxNORKcs...) Client: Now, let's rollback! Caretaker: Restoring state to: 2019-01-26 21:11:24 / (lHxNORKcs...) Originator: My state has changed to: lHxNORKcsgMWYnJqoXjVCbQLEIeiSp Client: Once more! Caretaker: Restoring state to: 2019-01-26 21:11:24 / (wQAehHYOq...) Originator: My state has changed to: wQAehHYOqVSlpEXjyIcgobrxsZUnat