TypeError: 'NoneType'对象不可迭代，函数返回结果未定义

Question

我在这一行代码“companyName, monthAverage, costPerTon, totalCost = displayCost(companyName, monthAverage, costPerTon, totalCost)”上遇到了“TypeError: 'NoneType' object is not iterable”的错误，我真搞不懂为什么会这样。

抱歉，我似乎无法正确格式化内容...

4-25-11

最终项目，全球垃圾项目

主函数

def main():

    #intialize variables
    endProgram = 'no'
    companyName = 'NONAME'

    #call to input company name
    companyName = inputName(companyName)

    #start 'end program' while loop
    while endProgram == 'no':

        #initializes variables
        companyName = 'NONAME'
        monthAverage = 0
        costPerTon = 0
        totalCost = 0
        yearTotal = 0

        #call to input company name
        companyName = inputName(companyName)

        #call to get the tonnage
        yearTotal, monthAverage = getTonnage(yearTotal, monthAverage)

        #call to calculate the cost
        monthAverage, costPerTon, totalCost, yearTotal = calculateCost(monthAverage, costPerTon, totalCost, yearTotal)

        #call to display the cost
        companyName, monthAverage, costPerTon, totalCost = displayCost(companyName, monthAverage, costPerTon, totalCost)

        endProgram = raw_input('Do you want to end the program? (enter yes or no)')

获取公司名称

def inputName(companyName):
    companyName = raw_input('What is the name of your company? ')
    return companyName

获取吨数

def getTonnage(yearTotal, monthAverage):
    yearTotal = input('How many tons of garbage are you dumping this year? ')
    monthAverage = yearTotal / 12
    return yearTotal, monthAverage

计算费用

def calculateCost(monthAverage, costPerTon, totalCost, yearTotal):
    if monthAverage > 100:
        costPerTon = 7000
    elif monthAverage > 50:
        costPerTon = 6500
    elif monthAverage > 20:
        costPerTon = 5500
    else:
        costPerTon = 4500
    totalCost = costPerTon * yearTotal
    return monthAverage, costPerTon, totalCost, yearTotal

打印费用

def displayCost(companyName, monthAverage, costPerTon, totalCost):
    print 'Dear',companyName
    print 'The average tonnage per month is ', monthAverage
    print 'The cost per ton is $',costPerTon
    print 'The total the is the cost per ton times total tons $',totalCost

运行主函数

main()

Answer 1

displayCost() 这个函数没有返回任何东西。

>>> a, b, c = None
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'NoneType' object is not iterable

Answer 2

你试图把 displayCost 函数的返回值拆分成 4 个变量，但 displayCost 并没有返回任何东西。在 Python 中，每个函数调用都会返回一些东西（或者抛出一个异常），如果没有返回值，就会返回 None。所以 None 是不能被拆分的。

你可能想要把：

companyName, monthAverage, costPerTon, totalCost = displayCost(companyName, monthAverage, costPerTon, totalCost)

改成：

displayCost(companyName, monthAverage, costPerTon, totalCost)