用python 设计一个 银行账户类:Account，该类包含三个属性：账号、用户名、余额。该类提供三个方法：存款、取款、转账。初始化时，账户余额为0，取款和转账前需判断余额是否充足，余额不足时，操作失败，输出相关提示信息。输出账户对象时，将会显示账号、用户名、余额等基本信息。

好的，下面是一个简单的实现：

class Account:
    def __init__(self, account_number, username):
        self.account_number = account_number
        self.username = username
        self.balance = 0

    def deposit(self, amount):
        self.balance += amount
        print("Deposit successful. Current balance: {}".format(self.balance))

    def withdraw(self, amount):
        if amount > self.balance:
            print("Withdrawal unsuccessful. Insufficient balance.")
        else:
            self.balance -= amount
            print("Withdrawal successful. Current balance: {}".format(self.balance))

    def transfer(self, amount, recipient):
        if amount > self.balance:
            print("Transfer unsuccessful. Insufficient balance.")
        else:
            self.balance -= amount
            recipient.balance += amount
            print("Transfer successful. Current balance: {}".format(self.balance))

    def __str__(self):
        return "Account number: {}\nUsername: {}\nBalance: {}".format(self.account_number, self.username, self.balance)

这个类有三个属性：账号、用户名和余额。初始化时余额为0。这个类提供了三个方法：存款、取款和转账。存款和取款会更新余额并输出当前余额。转账会检查账户余额是否充足并更新余额。如果余额不足，操作失败并输出相关提示信息。这个类还重载了 `__str__` 方法，以便在输出账户对象时显示账号、用户名和余额等基本信息。