ATM程序Python

Question

我在python中为一个简单的ATM程序提交了这段代码。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。我已尝试重写此功能一百万次，但当我做我的余额不更新。有人能告诉我我做错了什么吗？让我感到困扰的是我自己无法理解！

我原来的：

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")

我编辑的退出功能：

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

你永远不会更新＆＃34;全球＆＃34; balance使用withdraw ...

返回的金额

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())

此外，

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范围。

Answer 2

在withdraw()函数中，您不应该引用全局变量balance和amount。调用函数时，只需要更新balance，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())