Python 以外币存款的复利

我正在为一个comp sci班做作业。我觉得我真的很接近，但我不能完全得到答案。基本上，这个任务是一个复利计算器，我想做的是在初始投资中增加存款，允许某人在某一点停止支付，但在另一点收集。例如，“用户可能已经有
当他们开始计算退休金时，在他们的账户上存了10000美元。他们打算存钱
在接下来的10年里，每年再增加1000美元，届时他们将停止额外的收入
存入他们的帐户。但是，他们可能离退休还有20年。你的计划 应能够考虑这些不同的输入，并计算其正确的未来值
“退休账户”

以下是我目前的代码：

def main():
    print("Welcome to Letmeretire.com's financial retirement calculator!")

    import random
    num = random.randrange(10000)

    principal = int(input("How much are you starting with for your retirement savings?"))
    deposit = int(input("How much money do you plan to deposit each year?"))
    interest = int(input("How much interest will your account accrue annually"))
    time = int(input("Please enter the number of years that you plan to deposit money for."))
    time_till_retirement = int(input("How long until you plan on retiring? (Please enter this amount in years)"))
    t = time + 1
    APR = interest/100
    R = ((1+APR/12)**12)-1
    DR = deposit/R
    DRT = deposit/(R*(1+R)**time)
    PV = principal+(DR-DRT)
    future_value = PV*((1+APR/12)**12*time)
    if time < time_till_retirement:
        time1 = (time_till_retirement-time)
        future = future_value*((1+APR/12)**12*time1)
    else:
        future = future_value
    for i in range(1, t):
        print("After " + str(i) + " years you will have "+ str(future) + " saved!")

main()

---

我认为您需要确保公式正确：

FV（t）=5000*（1.12**t）+1000*（1.12**t）+1000*（1.12** （t-1））+…+1000 * 1.12 =5000*（1.12**t）+1000*（1.12**t-1）*1.12/0.12

然后我们可以定义一个函数：

def fv(t, initial, annual, interest_rate):
    return initial * (1+interest_rate) ** t + \
           annual * (1+interest_rate) * ((1+interest_rate) ** t - 1) / interest_rate

测试：

收益率：

6720.0
10803.968
15926.8974592

---

到目前为止，主要工作已经完成，我想你可以处理其余的工作。

在大多数情况下，我更喜欢雷的解析解——将值插入公式，得到最终答案，而不是逐年迭代

但是，在本例中，您需要每年的值，因此您不妨迭代：

import sys

# Python 2/3 compatibility shim
if sys.hexversion < 0x3000000:
    rng = xrange
    inp = raw_input
else:
    rng = range
    inp = input

def getter_fn(datatype):
    if datatype == str:
        return inp
    else:
        def fn(prompt=''):
            while True:
                try:
                    return datatype(inp(prompt))
                except ValueError:
                    pass
        return fn

get_float = getter_fn(float)
get_int   = getter_fn(int)

def main():
    print("Welcome to Letmeretire.com's financial retirement calculator!")

    principal  = get_float("Initial investment amount? ")
    periods    = get_int  ("How many years will you make an annual deposit? ")
    deposit    = get_float("Annual deposit amount? ")
    apr        = get_float("Annual interest rate (in percent)? ") / 100
    retirement = get_int  ("Years until retirement? ")

    deposits    = [deposit] * periods
    no_deposits = [0.] * (retirement - periods)

    amount = principal
    for yr, d in enumerate(deposits + no_deposits, 1):
        amount = (amount + d) * (1. + apr)
        print('After {:>2d} year{} you have:   $ {:>10.2f}'.format(yr, 's,' if yr > 1 else ', ', amount))

if __name__ == '__main__':
    main()

我有一个类似于上面提到的问题，但我不明白为什么方程（公式）的第二部分在第二个等号之后？ 还有没有其他更简洁的方法，而不必多次对该部分进行编码“

FV（t）=5000*（1.12**t）+1000*（1.12**t）+1000*（1.12**（t-1））

6720.0
10803.968
15926.8974592

import sys

# Python 2/3 compatibility shim
if sys.hexversion < 0x3000000:
    rng = xrange
    inp = raw_input
else:
    rng = range
    inp = input

def getter_fn(datatype):
    if datatype == str:
        return inp
    else:
        def fn(prompt=''):
            while True:
                try:
                    return datatype(inp(prompt))
                except ValueError:
                    pass
        return fn

get_float = getter_fn(float)
get_int   = getter_fn(int)

def main():
    print("Welcome to Letmeretire.com's financial retirement calculator!")

    principal  = get_float("Initial investment amount? ")
    periods    = get_int  ("How many years will you make an annual deposit? ")
    deposit    = get_float("Annual deposit amount? ")
    apr        = get_float("Annual interest rate (in percent)? ") / 100
    retirement = get_int  ("Years until retirement? ")

    deposits    = [deposit] * periods
    no_deposits = [0.] * (retirement - periods)

    amount = principal
    for yr, d in enumerate(deposits + no_deposits, 1):
        amount = (amount + d) * (1. + apr)
        print('After {:>2d} year{} you have:   $ {:>10.2f}'.format(yr, 's,' if yr > 1 else ', ', amount))

if __name__ == '__main__':
    main()

Welcome to the Letmeretire.com financial retirement calculator!
Initial investment amount? 5000
How many years will you make an annual deposit? 5
Annual deposit amount? 1000
Annual interest rate (in percent)? 12
Years until retirement? 10
After  1 year,  you have:   $    6720.00
After  2 years, you have:   $    8646.40
After  3 years, you have:   $   10803.97
After  4 years, you have:   $   13220.44
After  5 years, you have:   $   15926.90
After  6 years, you have:   $   17838.13
After  7 years, you have:   $   19978.70
After  8 years, you have:   $   22376.14
After  9 years, you have:   $   25061.28
After 10 years, you have:   $   28068.64

FV(t) = 5000 * (1.12 ** t) + 1000 * (1.12 ** t) + 1000 * (1.12 ** (t-1)) + ... + 1000 * 1.12 = 5000 * (1.12 ** t) + 1000 * (1.12 ** t - 1) * 1.12 / 0.12