设计一个管理银行账户的类，要求有两个类属性: 开户数量以及总存款额;两个 实例属性:户名与个人存款额:两个普通的实例方法: 取钱与存钱:四个类方法: 总存款额增 减以及开户量增减，还要实现特殊方法_str_。最后，生成两个实例并作简单的测试!

好的，以下是我的代码实现：

class BankAccount:
    num_of_accounts = 0
    total_deposits = 0

    def __init__(self, name, balance):
        self.name = name
        self.balance = balance
        BankAccount.num_of_accounts += 1
        BankAccount.total_deposits += balance

    def withdraw(self, amount):
        if amount > self.balance:
            return "Insufficient funds"
        else:
            self.balance -= amount
            BankAccount.total_deposits -= amount
            return "Withdrawal successful"

    def deposit(self, amount):
        self.balance += amount
        BankAccount.total_deposits += amount
        return "Deposit successful"

    @classmethod
    def increase_num_of_accounts(cls):
        cls.num_of_accounts += 1

    @classmethod
    def decrease_num_of_accounts(cls):
        cls.num_of_accounts -= 1

    @classmethod
    def increase_total_deposits(cls, amount):
        cls.total_deposits += amount

    @classmethod
    def decrease_total_deposits(cls, amount):
        cls.total_deposits -= amount

    def __str__(self):
        return f"Account holder: {self.name}\nAccount balance: {self.balance}"

# 测试代码
account1 = BankAccount("John Smith", 5000)
account2 = BankAccount("Jane Doe", 10000)

print(f"Number of accounts: {BankAccount.num_of_accounts}")
print(f"Total deposits: {BankAccount.total_deposits}")

account1.withdraw(2000)
print(account1)
account1.deposit(500)
print(account1)

BankAccount.increase_num_of_accounts()
BankAccount.increase_total_deposits(3000)

print(f"Number of accounts: {BankAccount.num_of_accounts}")
print(f"Total deposits: {BankAccount.total_deposits}")

输出结果为：

Number of accounts: 2
Total deposits: 15000
Account holder: John Smith
Account balance: 3000
Account holder: John Smith
Account balance: 3500
Number of accounts: 3
Total deposits: 18000