__str__;（self）函数不适用于在Python中打印对象

我一直在努力改进Python中类和对象的使用，但在程序中显示不同对象的值时遇到了问题。我的指导老师告诉我，每当对象被传递print（）函数时，就会自动调用使用str（self）函数，但是，输出仍然显示对象在内存中的地址，而不是值。我在下面记录了我的代码，并在两个不同的编译程序中运行了它，但仍然找不到错误发生的地方

# the class of the bank account
class BankAccount:
    def __init__(self, bal):
        self.__balance = bal

# deposits the amount given by the user
def deposit(self, amount):
    self.__balance += amount

# withdraws the amount given by the user
def withdraw(self, amount):
    if(self.__balance >= amount):
        self.__balance -= amount
    else:
        print("Error: Insufficient funds")

# returns the current balance of the user's account
def get_balance(self):
    return self.__balance

# sets the user's account given a specified balance
def set_balance(self, bal):
    self.__balance = bal

# prints the user's balance
def __str__(self):
    return "The balance is $" + format(self.__balance, ",.2f")

def main():
    start_bal = float(input("Enter your starting balance: ")) # retrieves balance from the user
    savings = BankAccount(start_bal) # creates an object that hold's the user's balance
    print(savings)

main()

程序输出的不是帐户的值，而是

---

请让我知道任何我可以更改以更正此问题的内容。谢谢。

您需要覆盖

BankAccount

类的

\uuuu str\uuuuu

运算符：

class BankAccount:
    def __init__(self, bal):
        self.__balance = bal

    def __str__(self):
        return "The balance is $" + format(self.__balance, ",.2f")


In [25]: start_bal = 2.3
In [27]: savings = BankAccount(start_bal) 

In [28]: print(savings)
The balance is $2.30

---

只需将方法正确嵌套在类中即可

这是一个缩进问题，您的类仅定义为：

# the class of the bank account
class BankAccount:
    def __init__(self, bal):
        self.__balance = bal

尝试将本节下的所有代码缩进一个独立块，直到进入

def main（）

函数，这样BankAccount就可以获得您想要的方法：

# the class of the bank account
class BankAccount:
    def __init__(self, bal):
        self.__balance = bal

    # deposits the amount given by the user
    def deposit(self, amount):
        self.__balance += amount

    # withdraws the amount given by the user
    def withdraw(self, amount):
        if(self.__balance >= amount):
            self.__balance -= amount
        else:
            print("Error: Insufficient funds")

    # returns the current balance of the user's account
    def get_balance(self):
        return self.__balance

    # sets the user's account given a specified balance
    def set_balance(self, bal):
        self.__balance = bal

    # prints the user's balance
    def __str__(self):
        return "The balance is $" + format(self.__balance, ",.2f")

def main():
    start_bal = float(input("Enter your starting balance: ")) # retrieves balance from the user
    savings = BankAccount(start_bal) # creates an object that hold's the user's balance
    print(savings)

main()

---

当调用main并在print（savings）中执行时，它将打印BankAccount类的str表示形式，该表示形式是储蓄内存地址，并且由于str实现是在类的外部定义的，因此它与类无关

试试这个：

# the class of the bank account
class BankAccount:
    def __init__(self, bal):
        self.__balance = bal

    # deposits the amount given by the user
    def deposit(self, amount):
        self.__balance += amount

    # withdraws the amount given by the user
    def withdraw(self, amount):
        if(self.__balance >= amount):
            self.__balance -= amount
        else:
            print("Error: Insufficient funds")

    # returns the current balance of the user's account
    def get_balance(self):
        return self.__balance

    # sets the user's account given a specified balance
    def set_balance(self, bal):
        self.__balance = bal

    # prints the user's balance
    def __str__(self):
        return "The balance is $" + format(self.__balance, ",.2f")

def main():
    start_bal = float(input("Enter your starting balance: ")) # retrieves balance from the user
    savings = BankAccount(start_bal) # creates an object that hold's the user's balance
    print(savings)

main()

---

您的格式有问题，需要缩进定义这些函数不在类内，只有

\uuuu init\uuu

在类内，您应该正确设置代码的格式谢谢大家！不过，我有一个问题。您知道为什么函数需要在类中缩进吗？为什么即使在程序中声明了它们，我也不能正确使用它们？