使用Python进行复利

我正在写一个测试，按年度返回利息总额。在我的Investor类中的数组

interest=[]

内的每个步骤上合成时，如何附加感兴趣的值？出于某种原因，我很难理解这一点

代码：

class Test(unittest.TestCase):

'''Represents my test case(s) for the dojo.'''

def setUp(self):
    '''Defines the initial state of an investor.'''
    self.investor = Investor(10000, 7.2, 5)

def test_solve_for_interest(self):
    self.assertEqual(self.investor.get_interest(), 720.0)

def test_get_interest_by_year(self):
    '''Returns a value of interest associated by the year.'''
    self.assertEqual(self.investor.interest_by_year(1), 10720.0)


class Investor(object):

    def __init__(self, amount, rate, time):
        self.amount = amount
        self.rate = rate
        self.time = time

    def get_interest(self):
        return (self.amount * self.rate) / 100.0

    def interest_by_year(self, year):
        interest = []
        for i in xrange(1, (self.time+1)):
            # collect compounding interest each year
        return interest[year]

year 1 = 10,720.00 (interest[1])

year 2 = 11491.84  (interest[2])

year 3 = 12319.25  (interest[3])

year 4 = 13206.24  (interest[4])

year 5 = 14157.09  (interest[5])

预期结果：

class Test(unittest.TestCase):

'''Represents my test case(s) for the dojo.'''

def setUp(self):
    '''Defines the initial state of an investor.'''
    self.investor = Investor(10000, 7.2, 5)

def test_solve_for_interest(self):
    self.assertEqual(self.investor.get_interest(), 720.0)

def test_get_interest_by_year(self):
    '''Returns a value of interest associated by the year.'''
    self.assertEqual(self.investor.interest_by_year(1), 10720.0)


class Investor(object):

    def __init__(self, amount, rate, time):
        self.amount = amount
        self.rate = rate
        self.time = time

    def get_interest(self):
        return (self.amount * self.rate) / 100.0

    def interest_by_year(self, year):
        interest = []
        for i in xrange(1, (self.time+1)):
            # collect compounding interest each year
        return interest[year]

year 1 = 10,720.00 (interest[1])

year 2 = 11491.84  (interest[2])

year 3 = 12319.25  (interest[3])

year 4 = 13206.24  (interest[4])

year 5 = 14157.09  (interest[5])

---

测试：

输出：

year 1 = 10720.0
year 2 = 11491.84
year 3 = 12319.25248
year 4 = 13206.2386586
year 5 = 14157.087842    

---

用熊猫可以更优雅地解决这个问题：

years = range(1,6)
rate = 0.072
rates = pandas.Series(index = years, data = rate)

请注意，这些年的利率可能有所不同

initialValue*((rates + 1).cumprod())

---

嗯，我得到了一个

AssertionError:72000.0！=10720.0

这样我的代码计算第一年利息为72000.0？您输入了正确的利率吗？对于测试，我知道是self.investor.interest，by，year，self.investor.interest，by，year（1），10720.0，但是作为我的测试，

intest，by，year（1）

输出了10720。所以我想知道你把速率设置为1.072对吗？我用7.2初始化了它，所以我需要把它除以100，然后加上1.0。另外，你能解释一下这背后的逻辑吗？这本应该是一个快速热身的道场，但它让我在准备最后一部分时遇到了不少麻烦。