$ python Main.py 
==== 0
Current status:[money = 100, fruits = []]
I have more money
The amount of money I have is now 200 yen
      (It has increased a lot, so let's save the current state)

==== 1
Current status:[money = 200, fruits = []]
fruits(Delicious grapes)I got
The amount of money I have is now 200 yen

==== 2
Current status:[money = 200, fruits = ['Delicious grapes']]
Nothing happened
The amount of money I have is now 200 yen

==== 3
Current status:[money = 200, fruits = ['Delicious grapes']]
I have more money
The amount of money I have is now 300 yen
      (It has increased a lot, so let's save the current state)


...(snip)


==== 22
Current status:[money = 500, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Apple', 'banana']]
fruits(Delicious banana)I got
The amount of money I have is now 500 yen

==== 23
Current status:[money = 500, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Apple', 'banana', 'Delicious banana']]
I have more money
The amount of money I have is now 600 yen
      (It has increased a lot, so let's save the current state)

==== 24
Current status:[money = 600, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Apple', 'banana', 'Delicious banana']]
Your money has been halved
The amount of money I have is now 300 yen

==== 25
Current status:[money = 300, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Apple', 'banana', 'Delicious banana']]
Nothing happened
The amount of money I have is now 300 yen

==== 26
Current status:[money = 300, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Apple', 'banana', 'Delicious banana']]
Your money has been halved
The amount of money I have is now 150 yen
      (It has decreased a lot, so let's return to the previous state)

==== 27
Current status:[money = 600, fruits = ['Delicious grapes', 'Delicious grapes', 'Delicious banana', 'Delicious apple', 'Delicious banana']]
Your money has been halved
The amount of money I have is now 300 yen

...(snip)

At the end, I was able to confirm the operation using the Memento pattern.

■ Details of sample program

Similar code has been uploaded to the Git repository. https://github.com/ttsubo/study_of_design_pattern/tree/master/Memento

--Directory structure

.
├── Main.py
└── memento
    ├── __init__.py
    ├── gamer.py
    └── memento.py

(1) The role of Originator

The ʻOriginator role creates a Memento role when you want to save your current state. The ʻOriginator role also, when passed the previous Memento role, returns to the state it was in when the Memento role was created. In the sample program, the Gamer class serves this role.

memento/gamer.py

import random
from memento.memento import Memento

class Gamer(object):
    def __init__(self, money):
        self.__fruitname = ["Apple", "Grape", "banana", "Mandarin orange"]
        self.__money = money
        self.__fruits = []

    def getMoney(self):
        return self.__money

    def bet(self):
        dice = random.randint(1, 6)
        if dice == 1:
            self.__money += 100
            print("I have more money")
        elif dice == 2:
            self.__money //= 2
            print("Your money has been halved")
        elif dice == 6:
            f = self.__getFruit()
            print("fruits({0})I got".format(f))
            self.__fruits.append(f)
        else:
            print("Nothing happened")

    def createMemento(self):
        m = Memento(self.__money)
        for f in self.__fruits:
            if f.startswith("Delicious"):
                m.addFruit(f)
        return m

    def restoreMemento(self, memento):
        self.__money = memento.money
        self.__fruits = memento.getFruits()

    def __str__(self):
        return "[money = {0}, fruits = {1}]".format(self.__money, self.__fruits)

    def __getFruit(self):
        prefix = ''
        if bool(random.getrandbits(1)):
            prefix = "Delicious"
        return prefix + random.choice(self.__fruitname)

(2) The role of Memento (souvenir)

The Memento role summarizes the internal information of the ʻOriginatorrole. TheMemento role has internal information about the ʻOriginator role, but that information is not disclosed to everyone. In the sample program, the Memento class serves this role.

memento/memento.py

class Memento(object):
    def __init__(self, money):
        self.money = money
        self.fruits = []

    def getMoney(self):
        return self.money

    def addFruit(self, fruit):
        self.fruits.append(fruit)

    def getFruits(self):
        return self.fruits

(3) The role of Caretaker

The Caretaker role tells the ʻOriginator role when you want to save the current state of the ʻOriginator role. The ʻOriginatorrole receives it, creates aMemento role, and passes it to the Caretakerrole. TheCaretaker role saves the Mementorole for future needs. In the sample program, thestartMain` method serves this role.

Main.py

import time
from memento.gamer import Gamer

def startMain():
    gamer = Gamer(100)
    memento = gamer.createMemento()

    for i in range(100):
        print("==== {0}".format(i))
        print("Current status:{0}".format(gamer))
        gamer.bet()
        print("The money you have{0}It became a circle".format(gamer.getMoney()))

        if gamer.getMoney() > memento.getMoney():
            print("      (It has increased a lot, so let's save the current state)")
            memento = gamer.createMemento()
        elif gamer.getMoney() < memento.getMoney() / 2:
            print("      (It has decreased a lot, so let's return to the previous state)")
            gamer.restoreMemento(memento)

        time.sleep(1)
        print("")

if __name__ == '__main__':
    startMain()

■ Reference URL

-[Finishing "Introduction to Design Patterns Learned in Java Language" (Not)](https://medium.com/since-i-want-to-start-blog-that-looks-like-men-do/java Introduction to Design Patterns Learned in Language-Finishing-Not-2cc9b34a30b2)