Question

我最近学过Python。我无法在此代码中捕获错误。有什么问题？

class BankAccount:

    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        self  = [initial_balance, 0]

    def deposit(self, amount):
        """Deposits the amount into the account."""
        self += amount

    def withdraw(self, amount):
        """
        Withdraws the amount from the account.  Each withdrawal resulting in a
        negative balance also deducts a penalty fee of 5 dollars from the balance.
        """
        self[0] -= amount
        if self[0] < 0:
            self[0] -= 5

        self[1] += 1

    def get_balance(self):
        """Returns the current balance in the account."""
        return self[0]

    def get_fees(self):
        """Returns the total fees ever deducted from the account."""
        return 5*self[1]


my_account = BankAccount(10)
my_account.withdraw(15)
my_account.deposit(20)
my_account.get_balance(), my_account.get_fees()

错误是：

Traceback (most recent call last):
  File "C:\Python34\bank.py", line 28, in <module>
    my_account.withdraw(15)
  File "C:\Python34\bank.py", line 15, in withdraw
    self[0] -= amount + 5
TypeError: 'BankAccount' object does not support indexing

self值包含initial_balance以及已提取的提款次数。

Answer 1

self总是指调用类函数的对象。因此，建议不要为自变量分配一些内容，如：

self = #something

在构造函数中。为该变量命名。像：

self.details = [initialbalance,0]

并在任何地方使用变量名称。

Answer 2

看起来应该是这样的：

class BankAccount:

    OVERDRAW_PENALTY = 5

    def __init__(self, opening_balance=0):
        self.balance = opening_balance
        self.withdrawals = 0

    def withdraw(self, amount):
        self.withdrawals += 1
        self.balance -= amount
        if self.balance < 0:
            self.balance -= self.OVERDRAW_PENALTY
        return amount

请注意，我使用self来访问实例和类属性，而不是尝试直接分配给它。另外，我已经考虑了＃34;魔术数字＆＃34; 5，所以发生的事情更清楚。

此外，您get_fees的实施方式不正确 - 无论是否收取费用，提款的数量目前都会增加。您应该单独存储self.overdrawn_withdrawals计数，或保留一个正在运行的self.fees属性。

最后，我已将return amount添加到withdraw的末尾 - 这可以让您执行以下操作：

account2.deposit(account1.withdraw(100))

轻松在BankAccount之间转账。

Answer 3

self指的是BankAccount对象。您需要分配和引用实例变量。

您的__init__()方法应该是这样的：

class BankAccount:
    def __init__(self, initial_balance):
        """Creates an account with the given balance."""
        self.balance  = initial_balance
        self.fees = 0
        self.withdrawals = 0

    def deposit(self, amount):
        """Deposits the amount into the account."""
        self.balance += amount

同样，withdraw()和get_balance()应引用self.balance，get_fees()应引用self.fees。

TypeError：object不支持索引

3 个答案: