在 Python 中传递参数

Question

我想弄清楚如何在 Python 中传递参数以及为什么我的代码不起作用。为什么说参数没有定义？我需要每个函数的参数才能相互交流。我只能通过将变量放在定义的主函数中来解决这个问题，这不是我设计程序的方式。

#make computer program that takes amount of doughnuts that customer
#wants to order.
#second, multiply the number of doughnuts the customer wants to order
#by the price and the sales tax.
#next, print the price of the doughnut with the sales tax
DOUGHNUT=1.75
SALES_TAX=0.08625

def getNumDoughnuts(numDoughnuts):
    numDoughnuts= raw_input("How many donuts would you like to order?")
    return numDoughnuts

def calculateDoughnutPrice(numDoughnuts, doughnutPrice):
    doughnutPrice=DOUGHNUT*float(numDoughnuts)
    return doughnutPrice

def calculateSalesTax(doughnutPrice, priceWithTax):
    taxAmount= (doughnutPrice*(SALES_TAX))
    priceWithTax= taxAmount+doughnutPrice
    return priceWithTax

def displayPrice(priceWithTax):
    print(priceWithTax)

def main():
    getNumDoughnuts(numDougnuts)
    calculateDoughnutPrice(numDoughnuts, doughnutPrice)
    calculateSalesTax(doughnutPrice, priceWithTax)
    displayPrice(priceWithTax)

main()

Answer 1

在main中，调用getNumDoughnuts时确实没有定义numDougnuts。 OTOH，后一个函数忽略了它的参数并且 returns 是一个值，main 又忽略了它。依此类推——您需要将参数与 return 值区分开来！

所以按正确的顺序排列你的程序将变成：

DOUGHNUT = 1.75
SALES_TAX = 0.08625

def getNumDoughnuts():
    numDoughnuts = raw_input("How many donuts would you like to order?")
    return numDoughnuts

def calculateDoughnutPrice(numDoughnuts):
    doughnutPrice = DOUGHNUT * float(numDoughnuts)
    return doughnutPrice

def calculateSalesTax(doughnutPrice):
    taxAmount = doughnutPrice*(SALES_TAX)
    priceWithTax = taxAmount + doughnutPrice
    return priceWithTax

def displayPrice(priceWithTax):
    print(priceWithTax)

def main():
    numDoughnuts = getNumDoughnuts()
    doughnutPrice = calculateDoughnutPrice(numDoughnuts)
    priceWithTax = calculateSalesTax(doughnutPrice)
    displayPrice(priceWithTax)

main()

看到参数和 return 值之间的区别了吗？参数是使进入函数的原因（并且它们的值必须在您调用该函数时定义）。 return 值是函数的 out 值——并且通常需要绑定到变量，或者由函数的调用者以其他方式使用。

还有，当然，你需要调用main，否则什么也不会发生！-)

在 Python 中传递参数

Passing Arguments in Python

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