类和实例

Question

我是 OOP 的新手，并且通过编写预算来练习 class 这样：

class Budget:
    category_record = []
    def __init__(self, category = '', balance = 0):
        self.category = category
        self.balance = balance
        
        Budget.category_record.append(self)
        
    
    def deposit(self, amount):
        self.balance += amount
        print(f"You have deposited {amount} into your {self.category} Budget, your balance is {self.balance}")
        return

    def withdraw(self, amount):
        if amount > self.balance:
            print('Insufficient Balance, unable to withdraw')
        else:
            self.balance -= amount
        print(f"You have withdrawn {amount} from your {self.category} Budget, your balance is {self.balance}")
        return 
    
    def category_balance(self):
        print(f'Your balance is {self.balance} for your {self.category} budget')

我试图记录所有预算实例class作为一种方法（如果我的条款有误，请原谅我，还在习惯它们）


# Instantiate Food budget 
food = Budget('food')

# deposit 200 into food budget
food.deposit(200)

# withdraw 100 from food budget
food.withdraw(100)

#instantaite rent budget
rent = Budget('house', 5000)

# check balance of rent budget
rent.category_balance()

这样当我在预算 class 上调用记录方法时，我可以获得 ['food'、'rent'] 的列表或者如果可能的话，一个字典，其中键作为类别，值作为余额 {'food':100...}

Answer 1

如果您想获得预算的所有实例的列表 class，您的方法可以 return 您已经在其中存储所有内容的 category_record 列表创建实例时。但是，您似乎希望列表包含要为其分配实例的变量的名称（标识符）。预算 class 将无法访问这些名称，因此，我建议您尝试使用类别名称，因为这些名称将记录在您的 category_record 变量中。

根据您的问题，我假设您希望调用该方法 record。最好的方法是使用带有内置 classmethod 装饰器的 class 方法。这些方法作用于 class 本身，而不是实例，因此采用 cls 参数而不是 self 参数（这两个名称只是约定俗成，但我强烈建议反对偏离惯例，因为这会使您的代码对其他人来说不必要地复杂）。例如：

class Budget:
    ...
    # other code
    ....
    category_record = []

    @classmethod
    def record(cls):
        return [budget.category for budget in cls.category_record]
        # If you are unfamiliar with this syntax, search up "list comprehensions"

# Access the list
print(Budget.category_record)

如果你想要一个字典，你可以用这个替换那个方法：

class Budget:
    ...
    # other code
    ...
    category_record = []

    @classmethod
    def record(cls):
        return {budget.category:budget.balance for budget in cls.category_record}
        # If you are unfamiliar with this syntax, search up "dictionary comprehensions"

# Access the dictionary
print(Budget.category_record)

Answer 2

详细说明我的@classmethod 评论：

class Budget:
    category_record = []
    def __init__(self, category = '', balance = 0):
        self.category = category
        self.balance = balance

        Budget.category_record.append(self)


    def deposit(self, amount):
        self.balance += amount
        print(f"You have deposited {amount} into your {self.category} Budget, your balance is {self.balance}")
        return

    def withdraw(self, amount):
        if amount > self.balance:
            print('Insufficient Balance, unable to withdraw')
        else:
            self.balance -= amount
        print(f"You have withdrawn {amount} from your {self.category} Budget, your balance is {self.balance}")
        return

    def category_balance(self):
        print(f'Your balance is {self.balance} for your {self.category} budget')

    @classmethod
    def budget_list(cls):
        if len(Budget.category_record)== 0:
            print("No budgets created")
        else:
            print("Budget Categories:")
            for budge in Budget.category_record:
                print(budge.category)

    @classmethod
    def full_report(cls):
        if len(Budget.category_record)== 0:
            print("No budgets created")
        else:
            print("Budget Balances:")
            for budge in Budget.category_record:
                print(f"{budge.category} : {budge.balance}")




# Instantiate Food budget
food = Budget('food')

# deposit 200 into food budget
food.deposit(200)

# withdraw 100 from food budget
food.withdraw(100)

#instantaite rent budget
rent = Budget('house', 5000)

# check balance of rent budget
rent.category_balance()

Budget.budget_list()

Budget.full_report()

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