EduCoder-Linux 与 Python编程2021-Python面向对象编程实训-第2关：三种贷款方式建模_本关的编程任务是,补全 7-2.py文件中 begin-end 区间的代码,实现用三种贷款方式建

任务描述

基于上一关实现的 Mortgage 类，利用继承机制，分别补全相关函数，实现用三种贷款方式建模的要求。

相关知识

基于上一关介绍的三种贷款方式：

固定利息率，不支付任何点；
固定利息率，支付一定的点；
可变利息率，低引诱利率，随后高利息率。
以 Mortgage 为父类，定义三个子类 Fixed 、 FixedWithPts 和 TwoRate ，这三个子类都利用基类 Mortgage 的 init 函数进行初始化，然后在 legend 属性上，填上自己的贷款类型描述。首先，TwoRate 类有两个利率，新增了 teaserRate 和 nextRate 两个属性，在 teaserRate 到期后，按 nextRate 利率支付利息。此外，FixedWithPts 在还贷之前，已经支付了一定比例的首付，其每月还贷金额是不同的。FixedWithPts 中的 pts 即为首次支付的比例，例如 20% ，则 pts 初始化为 20 。 TwoRate 的每月还贷金额分为两个时期，请注意这两个时期的利率是不一样的，分别为初始化函数中的 teaserRate 和 r 。

编程要求

本关的编程任务是，补全 7-2.py文件中 Begin-End 区间的代码，实现用三种贷款方式建模的要求。具体要求如下：

本关要求补全7-2.py文件中，3 个子类定义的 init 函数和 makePayment 函数，以实现三种贷款方式建模的功能；
具体请参见后续测试样例。
本关涉及的代码文件 7-2.py 的代码框架如下：

def findPayment(loan, r, m):
    return loan * ((r * (1 + r) ** m) / ((1 + r) ** m - 1))
class Mortgage(object):
     def __init__(self, loan, annRate, months):
         self.loan = loan
         self.rate = annRate / 1200.0
         self.months = months
         self.paid = [0.0]
         self.owed = [loan]
         self.payment = findPayment(loan, self.rate, self.months)
         self.legend = None
     def makePayment(self):
         self.paid.append(self.payment)
         reduction = self.payment - self.owed[-1] * self.rate
         self.owed.append(self.owed[-1] - reduction)
     def getTotalPaid(self):
         return sum(self.paid)
     def __str__(self):
         return str(self.legend)
class Fixed(Mortgage):
    def __init__(self, loan, r, months):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        #********** End *********#
        self.legend = 'Fixed, ' + str(r) + '%, for ' + str(months) + ' months'
class FixedWithPoints(Mortgage):
    def __init__(self, loan, r, months, pts):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        #********** End *********#
        self.legend = 'Fixed, ' + str(r) + '%, ' + str(pts) + ' points, for ' + str(months) + ' months'
class TwoRate(Mortgage):
    def __init__(self, loan, r, months, teaserRate, teaserMonths):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        #********** End *********#
        self.legend = str(teaserRate)\
                      + '% for ' + str(self.teaserMonths)\
                      + ' months, \n then ' + str(r) + '%, for ' + str(months) + ' months'
    def makePayment(self):
        # 请在此添加代码，补全函数makePayment
        #********** Begin *********#
        #********** End *********#
        Mortgage.makePayment(self)
if __name__=="__main__":
    print(Fixed(100000, 6.5, 36))
    print(Fixed(100000, 6.5, 120))
    print(FixedWithPoints(100000, 6.5, 36, 20))
    print(FixedWithPoints(100000, 6.5, 120, 20))
    print(TwoRate(100000, 9.0, 36, 4.8, 12))
    print(TwoRate(100000, 7.0, 120, 4.8, 36))
    
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测试说明

平台会对你编写的代码进行测试：

测试输入：

无输入

预期输出：

Fixed, 6.5%, for 36 months
Fixed, 6.5%, for 120 months
Fixed, 6.5%, 20 points, for 36 months
Fixed, 6.5%, 20 points, for 120 months
4.8% for 12 months,
then 9.0%, for 36 months
4.8% for 36 months,
then 7.0%, for 120 months
开始你的任务吧，祝你成功！

只要我们能梦想的，我们就能实现。

代码示例

def findPayment(loan, r, m):
    return loan * ((r * (1 + r) ** m) / ((1 + r) ** m - 1))
class Mortgage(object):
     def __init__(self, loan, annRate, months):
         self.loan = loan
         self.rate = annRate / 1200.0
         self.months = months
         self.paid = [0.0]
         self.owed = [loan]
         self.payment = findPayment(loan, self.rate, self.months)
         self.legend = None
     def makePayment(self):
         self.paid.append(self.payment)
         reduction = self.payment - self.owed[-1] * self.rate
         self.owed.append(self.owed[-1] - reduction)
     def getTotalPaid(self):
         return sum(self.paid)
     def __str__(self):
         return str(self.legend)
class Fixed(Mortgage):
    def __init__(self, loan, r, months):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        self.loan = loan
        self.r = r
        self.months = months
        #********** End *********#
        self.legend = 'Fixed, ' + str(r) + '%, for ' + str(months) + ' months'
class FixedWithPoints(Mortgage):
    def __init__(self, loan, r, months, pts):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        self.loan = loan
        self.pts = pts
        self.months = months
        #********** End *********#
        self.legend = 'Fixed, ' + str(r) + '%, ' + str(pts) + ' points, for ' + str(months) + ' months'
class TwoRate(Mortgage):
    def __init__(self, loan, r, months, teaserRate, teaserMonths):
        # 请在此添加代码，补全函数__init__
        #********** Begin *********#
        self.loan = loan
        self.r = r
        self.months = months
        self.teaserRate = teaserRate
        self.teaserMonths = teaserMonths
        #********** End *********#
        self.legend = str(teaserRate)\
                      + '% for ' + str(self.teaserMonths)\
                      + ' months, \n then ' + str(r) + '%, for ' + str(months) + ' months'
    def makePayment(self):
        # 请在此添加代码，补全函数makePayment
        #********** Begin *********#
        if len(self.paid) == self.teaserMonths + 1:
            self.rate = self.nextRate
            self.payment = findPayment(self.owed[-1], self.rate, self.months - self.teaserMonths)
        #********** End *********#
        Mortgage.makePayment(self)
if __name__=="__main__":
    print(Fixed(100000, 6.5, 36))
    print(Fixed(100000, 6.5, 120))
    print(FixedWithPoints(100000, 6.5, 36, 20))
    print(FixedWithPoints(100000, 6.5, 120, 20))
    print(TwoRate(100000, 9.0, 36, 4.8, 12))
    print(TwoRate(100000, 7.0, 120, 4.8, 36))

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