继续从类变量中获取NameError？

Question

因此，我试图通过创建一个类来全面理解Python，但是我对这个错误感到非常困惑。还在学习，所以请试着了解我的初学者在这里的情况。

  class Investor:

    def __init__(self, name, principle, returns):
        self.name = name
        self.principle = principle
        self.returns = returns 

    def info(self):
        return '{} {}'.format(self.name, self.principle)

    def deposit(self):
        global deposit_amount

        deposit_amount = float(input('Amount: '))
        return deposit_amount + self.principle + self.returns

    def withdraw(self):
        global withdraw_amount

        withdraw_amount = float(input('Withdraw amount: '))
        return self.principle + self.returns + deposit_amount - withdraw_amount

    def balance(self):
        if deposit_amount > 0 or withdraw_amount > 0:
            return self.principle + self.returns + deposit_amount - withdraw_amount
        else:
            return self.principle + self.returns



    


investor1 = Investor('John', 5000, 0)

while True:
    prompt = input('What would you like to do?\n')
    if prompt == 'Balance':
        try:
            print(investor1.balance())
        except ValueError:
            print(investor1.info())


    elif prompt == 'Deposit':
        print(investor1.deposit())

    elif prompt == 'Withdraw':
        print(investor1.withdraw())

输出：

What would you like to do?

当我第一次输入Deposit，然后是Withdraw和，然后是 Balance时，代码运行得非常好。

但是，当我首先输入Balance时，会得到以下错误：

return self.principle + self.returns + deposit_amount - withdraw_amount
NameError: name 'deposit_amount' is not defined

有什么帮助吗伙计们？

Answer 1

在调用global deposit_amount方法时，首先声明deposit(self)。该语句将变量放置在全局范围内。在调用deposit(self)之前，变量从未定义过，无论是在balance(self)的本地函数范围中还是在全局范围中。因此，您将得到此错误。这与OOP python一开始没有任何关系，但只是一个范围问题。要以面向对象的方式执行此操作，我建议您将变量作为类实例成员：

def __init__(self, name, principle, returns):
    self.name = name
    self.principle = principle
    self.returns = returns
    self.deposit_amount = 0
    self.withdraw_amount = 0

Answer 2

当您首先输入Balance时，deposit_amount和withdraw_amount都不会被定义，这两者都是balance定义中的if语句所需要的。

Answer 3

"deposit_amount“是函数存储的局部变量。所以除非你负责押金fn。首先，就系统而言，根本不存在。因此，尝试并初始化相同的全局。如果要阅读局部变量和全局变量，请参阅：https://www.tutorialspoint.com/global-and-local-variables-in-python#:~:text=There%20are%20two%20types%20of,function%20where%20it%20is%20defined。