迭代的Python问题

Question

import math 
import sys 

def calculateValues(loanAmt, numYears): 
    for monthlyRate in range (4, 9): 
     monthlyRate = monthlyRate/100 
     monthlyPayment = loanAmt * monthlyRate/(1 - math.pow(1/(1 + monthlyRate), numYears * 12)) 
     totalPayment = monthlyPayment * numYears * 12 
     return monthlyRate, monthlyPayment, totalPayment 

def printPayments(monthlyRate, monthlyPayment, totalPayment, loanAmt, numYears): 
    print("Rate Monthly Payment Total Payment") 
    for monthlyRate in range (4, 9): 
     calculateValues(loanAmt, numYears) 
     print("{0}%  ${1:0.2f}   ${2:0.2f}".format(monthlyRate, monthlyPayment, totalPayment)) 

def repeat(): 
    question = str(input("Would you like to create a new table? (Enter y for yes): ")) 
    if (question == "y"): 
     main() 
    else: 
     sys.exit() 

def getPositiveFloat(): 
    loanAmt = int(input("Enter the amount of the loan: ")) 
    numYears = int(input("Enter the number of years: ")) 
    if (loanAmt < 0) or (numYears < 0): 
     print("Please enter a positive number for both questions") 
     main() 
    return loanAmt, numYears 

def main(): 
    loanAmt, numYears = getPositiveFloat() 
    monthlyRate, monthlyPayment, totalPayment = calculateValues(loanAmt, numYears) 
    printPayments(monthlyRate, monthlyPayment, totalPayment, loanAmt, numYears) 
    repeat() 

main() 

当这个程序运行时，monthlyRate变量（在printPayments中定义）迭代，但calculateValues中计算的值不会迭代。我发现我需要给monthlyRate计算值作为参数，但我不确定如何做到这一点，没有一切都打破。

Answer 1

这是容易的，如果你的代码是因为你已经输入了有你的return语句缩进太多

def calculateValues(loanAmt, numYears): 
    myAnswer = [] 
    for monthlyRate in range (4, 9): 
     monthlyRate = monthlyRate/100 
     monthlyPayment = loanAmt * monthlyRate/(1 - math.pow(1/(1 + monthlyRate), numYears * 12)) 
     totalPayment = monthlyPayment * numYears * 12 
     thisRound = (monthlyRate, monthlyPayment, totalPayment) 
     myAnswer.append(thisRound) 
    return myAnswer 

它应该看起来像上面你是第一次迭代之后返回

我只是在这里猜测你想要每次迭代的结果，你需要将它们保存在某个容器中。我个人会将它们保存在字典中，但没有准备好，直到您的目标更清晰为止

您应该考虑一件事，直到您更舒适为止，可以在函数中添加一些打印语句，以便您可以查看数值每次迭代

def testFunction(somevalue): 
    for x in range(0, somevalue): 
     print 'hello' 
    return x 

y = testFunction(2) 

hello 
hello 
>>>y 
1 

Answer 2

问题是，您的代码第一次遇到“返回”语句时，它将返回值并离开函数。看起来你正在用printRayments循环monthlyRate（monthlyRate = [4，5，6，7，8]）。没关系。现在对于您的calculateValues函数，您希望将monthlyPayment和totalPayment返回给调用函数。您还需要将monthlyRate作为参数传入。

def calculateValues(monthlyRate, loanAmt, numYears): 
    monthlyRate = monthlyRate/100 
    monthlyPayment = loanAmt * monthlyRate \ 
       /(1 - math.pow(1/(1 + monthlyRate), numYears * 12)) 
    totalPayment = monthlyPayment * numYears * 12 
    return (monthlyPayment, totalPayment) 

def printPayments(monthlyRate, monthlyPayment, totalPayment, loanAmt, numYears): 
    print("Rate Monthly Payment Total Payment") 
    for monthlyRate in range (4, 9): 
     monthlyPayment, totalPayment = calculateValues(monthlyRate, loanAmt, numYears) 
     print("{0}%  ${1:0.2f}   ${2:0.2f}".format(monthlyRate, \ 
       monthlyPayment, totalPayment)) 

一般情况下，它看起来像你需要做一堆的阅读和思考如何写在计算机编程功能，特别是其中一个变量可以在程序的执行过程中看到。下面是这种阅读可能有用的链接：

http://gettingstartedwithpython.blogspot.com/2012/05/variable-scope.html

希望这有助于。

Answer 3

代码中有几个问题，您可以通过使用下面的代码执行比较来轻松查看。

1. calculateValues：循环运行，并返回在第一次循环
2. printPayments调用calculateValues但不拿起结果（这就是为什么在同一行再次印刷，再
3. printPayments结果也打印在一个循环中 - 这意味着有一个不需要的循环
4. main（）调用calculateValues然后printPayments - 这意味着两个for循环再次调用的次数太多而不保存结果

这里的固定码：

import math 
import sys 

def calculateValues(monthlyRate, loanAmt, numYears): 
    monthlyRate = monthlyRate/100 
    monthlyPayment = loanAmt * monthlyRate/(1 - math.pow(1/(1 + monthlyRate), numYears * 12)) 
    totalPayment = monthlyPayment * numYears * 12 
    return monthlyRate, monthlyPayment, totalPayment 

def printPayments(loanAmt, numYears): 
    print("Rate Monthly Payment Total Payment") 
    for monthlyRate in range (4, 9): 
     monthlyRate, monthlyPayment, totalPayment = calculateValues(monthlyRate, loanAmt, numYears) 
     print("{0}%  ${1:0.2f}   ${2:0.2f}".format(int(monthlyRate*100, monthlyPayment, totalPayment)) 

def repeat(): 
    question = str(input("Would you like to create a new table? (Enter y for yes): ")) 
    if (question == "y"): 
     main() 
    else: 
     sys.exit() 

def getPositiveFloat(): 
    loanAmt = int(input("Enter the amount of the loan: ")) 
    numYears = int(input("Enter the number of years: ")) 
    if (loanAmt < 0) or (numYears < 0): 
     print("Please enter a positive number for both questions") 
     main() 
    return loanAmt, numYears 

def main(): 
    loanAmt, numYears = getPositiveFloat() 
    printPayments(loanAmt, numYears) 
    repeat() 

main() 

OUTPUT：

Enter the amount of the loan: 100 
Enter the number of years: 20 
Rate Monthly Payment Total Payment 
4%  $4.00   $960.08 
5%  $5.00   $1200.01 
6%  $6.00   $1440.00 
7%  $7.00   $1680.00 
8%  $8.00   $1920.00 
Would you like to create a new table? (Enter y for yes): 

我觉得这事是错在你算算这里的利益的方式：

monthlyPayment = loanAmt * monthlyRate/(1 - math.pow(1/(1 + monthlyRate), numYears * 12)) 

但这部分我会让你自己解决;）