使用Python进行复利

Question

我正在写一个测试，它可以按年份返回利息总额。在我的Investor类的数组interest = []内的每一步合成时，如何添加感兴趣的值？由于某些原因，这一直很难让我的头脑。在

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]

预期结果：

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Answer 1

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，这一比率可能会在不同年份有所不同

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Answer 2

def interest_by_year(self, year):
    interest = [self.amount]
    for i in xrange(self.time):
        interest.append(interest[i]*self.rate)
    return interest[year]

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测试：

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输出：

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