python - python 2.7.3 中的函数和参数

Question

在我的计算机科学课上，我才刚刚开始学习 python 中的函数和参数。现在我的导师正在让我们学习参数传递。我没有输入大量的程序摘要，而是重新输入了下面的作业指南。

描述:在此程序中，用户必须选择输入费用、输入付款或显示信用卡余额。允许用户通过在键盘上输入代码来表明他们的选择。

使用以下函数名称:

• enterValue 用户输入一个值

• addCharge 将传递给函数的值添加到余额中

• addPayment从余额中减去传递给函数的值

• showBalance 显示信用卡当前余额

让用户输入以下代码以进行适当的操作:

• “C”用于输入费用

• 用于输入付款的“P”

• “B”表示余额

• 在输入“Z”之前允许输入交易

程序

balance = 0
def enterValue ():
    enter = input ("Enter a value.")
    return enter

def addCharge (enter,balance):
    balance = balance + enter
    return balance

def addPayment (enter,balance):
    balance = balance - enter
    return balance
def showBalance ():
    print "Your balance is... ", balance


transaction = raw_input ("Enter C for charges, P for payments, and B to show your balance. ") 
enterValue ()
while transaction != "Z":


    if transaction == "C":
        balance = addCharge(enter,balance)
        showBalance()        
    elif transaction == "P": 
        balance = addPayment (enter,balance)
        showBalance()
    elif transaction =="B":
        balance = enterValue()
        showBalance()
    transaction = raw_input ("Enter C for charges, P for payments, and B to show your balance. ") 

输出

Enter C for charges, P for payments, and B to show your balance. P

Traceback (most recent call last):
  File "/Users/chrisblive/Downloads/Charge_Braverman-2.py", line 26, in <module>
    balance = addPayment (enter,balance)
NameError: name 'enter' is not defined

(我的问题是我在 enterValue() 中的值没有被定义。)

Answer 1

练习的主要内容是了解将参数传递给函数。因此，只需将函数中所有需要的变量传递给它即可!大致上你可以说所有函数都有自己的命名空间，如果你想在其中使用另一个级别的值，你必须将它作为参数传递并返回它，如果你想在较低级别重用它。

例如:

###   Level "enterValue"   ###
def enterValue():
    return float(raw_input("Enter a value: "))
### End Level "enterValue" ###

###   Level "addCharge"   ###
def addCharge(enter, balance):
    balance = balance + enter
    return balance
### End Level "addCharge" ###

###   Level "showBalance"   ###
def showBalance(balance):
    print "Your balance is %f" % balance
### End Level "showBalance" ###

### Level "Mainlevel" ###
# This is where your program starts.
transaction = None
balance = 0.0
while transaction != "Z":
    transaction = raw_input("Enter C for charges, P for payments, and B to show your balance.\nEnter Z to exit: ").upper()

    if transaction == "C":
        enter = enterValue()
        balance = addCharge(enter, balance)
        showBalance(balance)
    elif transaction == "P":
        balance = addPayment(enter, balance)
        showBalance(balance)
    elif transaction == "B":
        showBalance(balance)
### End Level "Mainlevel" ###