自动柜员机程序Python

Question

我用python提交了一个简单的自动取款机程序的代码。我得到了充分的信任，但被告知不要使用全局变量，因为它们被认为是糟糕的编程。我已经试着重写这个函数一百万次了，但是当我重写的时候，我的余额没有更新。有人能告诉我我哪里做错了吗？我自己也搞不清楚这件事，这让我很困扰！

我的原创：

name=input("Name on your bank account? ")
balance=float(input("Your current balance? "))

def printMenu():
    print(name,"Welcome to the Lots of Money Bank")
    print("Enter 'b'(balance), 'd'(deposit), 'w'(withdraw), or'q'(quit)")

def getTransaction():
    transaction=str(input("What would you like to do? "))
    return transaction

def withdraw(bal,amt):
    global balance
    balance=bal-amt
    if balance<0:
        balance=balance-10

def formatCurrency(amt):
    return "$%.2f" %amt

###MAIN PROGRAM###

printMenu()
command=str(getTransaction())

while command!="q":
    if (command=="b"):
        print(name,"Your current balance is",formatCurrency(balance))
        printMenu()
        command=str(getTransaction())
    elif (command=="d"):
        amount=float(input("Amount to deposit? "))
        balance=balance+amount
        printMenu()
        command=str(getTransaction())
    elif (command=="w"):
        amount=float(input("Amount to withdraw? "))
        withdraw(balance,amount)
        printMenu()
        command=str(getTransaction())
    else:
        print("Incorrect command. Please try again.")
        printMenu()
        command=str(getTransaction())

print(name,"Goodbye! See you again soon")

我编辑过的取款功能：

def withdraw(bal,amt):
    bal=balance
    amt=amount
    if(bal<0):
        bal=bal-10
    else:
        bal=bal-amt
    return bal

and my edited elif
elif (command=="w"):
        amount=float(input("Amount to withdraw? "))
        withdraw(balance,amount)
        printMenu()
        command=str(getTransaction())

Answer 1

您从不使用从withdraw返回的数量来更新“全局”balance ...

试试这个：

# and my edited elif
elif (command=="w"):
        amount=float(input("Amount to withdraw? "))
        # update balance!
        balance = withdraw(balance,amount)
        printMenu()
        command=str(getTransaction())

另外，

def withdraw(bal,amt):
    # 'balance' is bound to global balance - we don't want to use that
    # this is why we have 'bal' (passed through parameters)
    # bal = balance # no need, bal=balance when function is called
    # amt=amount    # same as balance
    if(bal<0):
        bal=bal-10
    else:
        bal=bal-amt
    return bal

确保您了解程序中不同参数的作用域。

Answer 2

在withdraw()函数中，不应该引用全局变量balance和amount。当函数被调用时，只有balance需要更新，所以我们有：

def withdraw(bal,amt):
    if(bal<0):
        bal=bal-10
    else:
        bal=bal-amt
    return bal

和

elif (command=="w"):
        amount=float(input("Amount to withdraw? "))
        balance = withdraw(balance,amount)
        printMenu()
        command=str(getTransaction())