在python中，当我取款然后存款时，如何更新余额？

我正在使用python代码创建一个ATM，我需要创建存款和取款函数，它们的行为就像ATM一样。另外，存款和取款功能也可以工作。但是，当我先取款再存款时，余额不会更新。存款和取款都是一样的

谢谢你，非常感谢你的帮助

balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    counter = 0
    while counter <= 2:
        while counter == 0:
            withdraw = int(input("Enter the amount you want to withdraw: AED "))
            counter = counter + 1
        while ((int(balance) - int(withdraw)) < 0):
            print("Error Amount not available in card.")
            withdraw = int(input("Please enter the amount you want to withdraw again: AED "))
            continue
        while ((float(balance) - float(withdraw)) >= 0):
            print("Amount left in your account: AED" + str(balance - withdraw))
            return (balance - withdraw)
        counter = counter + 1


def deposit():
    counter = 0
    while counter <= 2:
        while counter == 0:
            deposit = int(input("Enter amount to be deposited: "))
            counter = counter + 1
        while ((int(balance) + int(deposit)) >= 0):
            print("Amount left in your account: AED" + str(balance + deposit))
            return (balance + deposit)
        counter = counter + 1

withdraw()
deposit()

余额=600
def draw（）：#请求提取金额，从余额中提取金额，返回余额金额
计数器=0
当计数器=0时）：
打印（“账户剩余金额：AED”+str（余额-提取））
退货（余额-提取）
计数器=计数器+1
def存款（）：
计数器=0
当计数器=0时）：
打印（“账户剩余金额：AED”+str（余额+存款））
退货（余额+押金）
计数器=计数器+1
撤回
存款（）

---

---

如果我提取17，余额将为583。但是，当我存入12英镑时，余额变成了612英镑，这是错误的，应该是595英镑。

你只是忘记保存新的余额，你只是把它打印出来

balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    while True:
        withdraw = int(input("Enter amount to be withdrawn: "))
        if withdraw > balance:
            print("Error Amount not available in card.")
        else: 
            new_balance = balance - withdraw
            print("Amount left in your account: AED" + str(new_balance))
            return (new_balance)

def deposit():
    deposit = int(input("Enter amount to be deposited: "))
    new_balance = balance + deposit
    print("Amount left in your account: AED" + str(new_balance))
    return (new_balance)

# This is the only place you HAVE to change for it to work
balance = withdraw()
balance = deposit()   

虽然有点随意改变，但最重要的是，你应该保持新的平衡

我还建议在将整数转换为整数之前检查它是否为int，从而使整数转换更安全

draw\u string=输入（“输入要提取的金额：”）
尝试：
撤销int=int（撤销字符串）
这是真的吗
除值错误外：
打印（“无效输入”）
is_int=False
如果为_int==True：

您根本没有更改“余额”变量！ 您的代码应该类似于：

balance = withdraw()
balance = deposit()

但是，您的代码还有许多其他问题。 首先，你不应该做那么多的演员。您必须将用户输入转换为一个数字，然后使用该类型计算所有内容。 您使用的是float和int。如果您想使用currency，您应该使用decimal（），因为在某些特殊情况下（您需要四舍五入），浮点运算不精确，而integer显然不提供浮点运算

此外，您的特殊“while”用法不符合常见的编码标准，使您的代码难以阅读。最好编写一个函数来获取用户输入，并将其与取款（）和存款（）逻辑分离

编辑：因为你似乎是一个初学者，我将提供一个最低限度的工作解决方案

import decimal

balance = 600

def get_user_input(action):
  # Get user input and convert it to decimal type
  return decimal.Decimal(input("Please enter amount to {} from your account: ".format(action)))

def withdraw():
  amount = get_user_input("withdraw")
  return balance - amount

def deposit():
  amount = get_user_input("deposit")
  return balance + amount

print("Your Balance is {} AED".format(balance))
balance = withdraw()
balance = deposit()
print("Your Balance is {} AED".format(balance))

---

我同意@Chetan Ranpariya的建议，您没有更改代码中两个函数的

余额
变量。您可以使用表达式
balance+=
、
balance-=
或
balance=balance+
等更改
balance
变量

balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    counter = 0
    while counter <= 2:
        while counter == 0:
            withdraw = int(input("Enter the amount you want to withdraw: AED "))
            counter = counter + 1
        while ((int(balance) - int(withdraw)) < 0):
            print("Error Amount not available in card.")
            withdraw = int(input("Please enter the amount you want to withdraw again: AED "))
            continue
        while ((float(balance) - float(withdraw)) >= 0):
            print("Amount left in your account: AED" + str(balance - withdraw))
            return (balance - withdraw)
        counter = counter + 1


def deposit():
    counter = 0
    while counter <= 2:
        while counter == 0:
            deposit = int(input("Enter amount to be deposited: "))
            counter = counter + 1
        while ((int(balance) + int(deposit)) >= 0):
            print("Amount left in your account: AED" + str(balance + deposit))
            return (balance + deposit)
        counter = counter + 1

balance = withdraw()
balance = deposit()

余额=600
def draw（）：#请求提取金额，从余额中提取金额，返回余额金额
计数器=0
当计数器=0时）：
打印（“账户剩余金额：AED”+str（余额-提取））
退货（余额-提取）
计数器=计数器+1
def存款（）：
计数器=0
当计数器=0时）：
打印（“账户剩余金额：AED”+str（余额+存款））
退货（余额+押金）
计数器=计数器+1
余额=支取（）
余额=存款（）
您没有更改
余额
变量，您只返回添加或减少的
存款
或
取款
的值

请尝试更改代码，以便在返回新的
余额之前将其保存。因此，不是：

print("Amount left in your account: AED" + str(balance - withdraw))
return (balance - withdraw)

尝试：

然后对
存款
功能执行相同操作

您的新代码：

balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    counter = 0
    while counter <= 2:
        while counter == 0:
            withdraw = int(input("Enter the amount you want to withdraw: AED "))
            counter = counter + 1
        while ((int(balance) - int(withdraw)) < 0):
            print("Error Amount not available in card.")
            withdraw = int(input("Please enter the amount you want to withdraw again: AED "))
            continue
        while ((float(balance) - float(withdraw)) >= 0):
            balance = (balance - withdraw)
            print("Amount left in your account: AED" + str(balance))
            return balance
        counter = counter + 1


def deposit():
    counter = 0
    while counter <= 2:
        while counter == 0:
            deposit = int(input("Enter amount to be deposited: "))
            counter = counter + 1
        while ((int(balance) + int(deposit)) >= 0):
            balance = (balance + deposit)
            print("Amount left in your account: AED" + str(balance))
            return balance
        counter = counter + 1

withdraw()
deposit()

余额=600
def draw（）：#请求提取金额，从余额中提取金额，返回余额金额
计数器=0
当计数器=0时）：
余额=（余额-提取）
打印（“账户剩余金额：AED”+str（余额））
返回余额
计数器=计数器+1
def存款（）：
计数器=0
当计数器=0时）：
余额=（余额+存款）
打印（“账户剩余金额：AED”+str（余额））
返回余额
计数器=计数器+1
撤回
存款（）
在
deposit（）
和
widthdraw（）
函数中，您从未实际接触到保持平衡的变量，这就是为什么您看不到变化

您已经定义了变量balance，但您从未使用
balance=balance-x
更新过该值。您仅使用
str（余额+存款）
打印该数学运算的结果，该代码实际上不会改变您的余额

要更改平衡，您需要使用
balance+=widthdraw
更新该全局变量。但如果将该代码放入代码中，则会出现以下错误：

UnboundLocalError:分配前引用的局部变量“balance”

这是因为为了从函数内部更新全局变量，需要使用global关键字，以便链接到全局变量

下面的代码现在可以工作了，下面是两行重要的代码：

balance -= withdraw
balance += deposit

这就是您实际修改balance变量中的值的方式，而不仅仅是查看数学运算的输出

balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    global balance
    counter = 0
    while counter <= 2:
        while counter == 0:
            withdraw = int(input("Enter the amount you want to withdraw: AED "))
            counter = counter + 1
        while ((int(balance) - int(withdraw)) < 0):
            print("Error Amount not available in card.")
            withdraw = int(input("Please enter the amount you want to withdraw again: AED "))
            continue
        while ((float(balance) - float(withdraw)) >= 0):
            balance -= withdraw
            print("Amount left in your account: AED " + str(balance))
            return (balance)
        counter = counter + 1


def deposit():
    global balance
    counter = 0
    while counter <= 2:
        while counter == 0:
            deposit = int(input("Enter amount to be deposited: "))
            counter = counter + 1
        while ((int(balance) + int(deposit)) >= 0):
            balance += deposit
            print("Amount left in your account: AED" + str(balance))
            return balance
        counter = counter + 1

withdraw()
deposit()

让我们一点一点地看一遍

装饰师是这样的

def exit_on_input_cast_error(func):
    def wrapper(arg):
        try:
            return func(arg)
        except ValueError as ex:
            print("Exiting, bye.")
            exit()
    return wrapper

这只是装饰器的语法。重要的部分是返回函数（arg）。这就是将被捕获的函数。因此，这个decorator只负责捕获ValueError异常，当您尝试转换
int（'
balance = 600

def withdraw():  # asks for withdrawal amount, withdraws amount from balance, returns the balance amount
    counter = 0
    while counter <= 2:
        while counter == 0:
            withdraw = int(input("Enter the amount you want to withdraw: AED "))
            counter = counter + 1
        while ((int(balance) - int(withdraw)) < 0):
            print("Error Amount not available in card.")
            withdraw = int(input("Please enter the amount you want to withdraw again: AED "))
            continue
        while ((float(balance) - float(withdraw)) >= 0):
            tmp_balance -= withdraw
            print("Amount left in your account: AED " + str(tmp_balance))
            return tmp_balance
        counter = counter + 1


def deposit():
    counter = 0
    while counter <= 2:
        while counter == 0:
            deposit = int(input("Enter amount to be deposited: "))
            counter = counter + 1
        while ((int(balance) + int(deposit)) >= 0):
            tmp_balance += deposit
            print("Amount left in your account: AED" + str(tmp_balance))
            return tmp_balance
        counter = counter + 1

balance = withdraw()
balance = deposit()

def exit_on_input_cast_error(func):
def wrapper(arg):
    try:
        return func(arg)
    except ValueError as ex:
        print("Exiting, bye.")
        exit()
return wrapper


class ATM():
"""A simple atm machine"""

def __init__(self, balance):
    self.cash_available = balance

@exit_on_input_cast_error
def withdraw(self):
    '''Withdraws entered amount, until user exits'''
    continue_withdraw = True
    while continue_withdraw:
        withdraw_amount = self._get_withdraw_input()
        self.cash_available -= withdraw_amount
        self.print_balance("left in")
        withdraw_again = str(input("Would you like to withdraw another amount? (Y or N)"))
        continue_withdraw = withdraw_again.lower() in ['1', 'y', 'yes']
    self.print_bye()

@exit_on_input_cast_error
def _get_withdraw_input(self):
    input_error = True
    while input_error:
        withdrawl = int(input("Enter the amount you want to withdraw (Press N to exit): AED "))

        if (self.cash_available - withdrawl) < 0:
            print("Error Amount not available in machine.")
            input_error = True
        elif (self.cash_available - withdrawl) > self.cash_available:
            print("Error, you can't withdraw a negative amount.")
            input_error = True
        else:
            input_error = False
    return withdrawl

@exit_on_input_cast_error
def deposit(self):
    input_error = True
    while input_error:
        depositing = int(input("Please enter the amount you want to deposit (Press N to exit): AED "))
        if (self.cash_available + depositing) < self.cash_available:
            print("You cannot deposit a negative amount.")
        else:
            input_error = False
            self.cash_available += depositing
    self.print_balance("now in")
    self.print_bye()

def print_balance(self, custom_insert = 'in'):
    print(f"Amount {custom_insert} your account: AED {self.cash_available}")

def print_bye(self):
    print("Thank you for using our services today, bye.")

def exit_on_input_cast_error(func):
    def wrapper(arg):
        try:
            return func(arg)
        except ValueError as ex:
            print("Exiting, bye.")
            exit()
    return wrapper

class ATM():
"""A simple atm machine"""

def __init__(self, balance):
    self.cash_available = balance

@exit_on_input_cast_error
def _get_withdraw_input(self):
    input_error = True
    while input_error:
        withdrawl = int(input("Enter the amount you want to withdraw (Press N to exit): AED "))

        if (self.cash_available - withdrawl) < 0:
            print("Error Amount not available in machine.")
            input_error = True
        elif (self.cash_available - withdrawl) > self.cash_available:
            print("Error, you can't withdraw a negative amount.")
            input_error = True
        else:
            input_error = False
    return withdrawl

while there's an error do the following:
    Get the user input and cast it as an int. 
    Make sure the amount user has introduced matches the following criteria:
        It is not more than the cash available in the atm.
        It is not a negative number.

withdrawl = int(input("Enter the amount you want to withdraw (Press N to exit): AED "))

@exit_on_input_cast_error
def withdraw(self):
    '''Withdraws entered amount, until user exits'''
    continue_withdraw = True
    while continue_withdraw:
        withdraw_amount = self._get_withdraw_input()
        self.cash_available -= withdraw_amount
        self.print_balance("left in")
        withdraw_again = str(input("Would you like to withdraw another amount? (Y or N)"))
        continue_withdraw = withdraw_again.lower() in ['1', 'y', 'yes']
    self.print_bye()

while the user wants to withdraw:
    Get the user input
    Check that the withdraw action does not result in 0 or negative number. 
    Print the balance
    Ask the user if they want to withdraw again.

def print_balance(self, custom_insert = 'in'):
    print(f"Amount {custom_insert} your account: AED {self.cash_available}")

def print_bye(self):
    print("Thank you for using our services today, bye.")

@exit_on_input_cast_error
def deposit(self):
    input_error = True
    while input_error:
        depositing = int(input("Please enter the amount you want to deposit (Press N to exit): AED "))
        if (self.cash_available + depositing) < self.cash_available:
            print("You cannot deposit a negative amount.")
        else:
            input_error = False
            self.cash_available += depositing
    self.print_balance("now in")
    self.print_bye()

atm_a = ATM(600)
atm_a.withdraw()

Enter the amount you want to withdraw (Press N to exit): AED 100
Amount left in your account: AED 500
Would you like to withdraw another amount? (Y or N)Y
Enter the amount you want to withdraw (Press N to exit): AED -1
Error, you can't withdraw a negative amount.
Enter the amount you want to withdraw (Press N to exit): AED 501
Error Amount not available in machine.
Enter the amount you want to withdraw (Press N to exit): AED 5
Amount left in your account: AED 495
Would you like to withdraw another amount? (Y or N)yes
Enter the amount you want to withdraw (Press N to exit): AED 5
Amount left in your account: AED 490
Would you like to withdraw another amount? (Y or N)no
Thank you for using our services today, bye.

atm_a = ATM(600)
atm_a.withdraw()
atm_a.deposit()

Enter the amount you want to withdraw (Press N to exit): AED 500
Amount left in your account: AED 100
Would you like to withdraw another amount? (Y or N)no
Thank you for using our services today, bye.
Please enter the amount you want to deposit (Press N to exit): AED -1
You cannot deposit a negative amount.
Please enter the amount you want to deposit (Press N to exit): AED 1000
Amount now in your account: AED 1100
Thank you for using our services today, bye.