如何找出循环中的输出数量？

Question

我是 python 的初学者，我正在为我的一项（简单的）大学作业而苦苦挣扎。 我得到了以下指示：

一家银行提供一个储蓄账户，每年收取费用。 编写一个程序，让用户输入

1. 初始投资。

2. 以百分比表示的年利率。

3. 年费。

然后，程序应计算投资翻倍所需的时间。 利息每年增加一次。

程序运行示例：

输入投资：1000

输入利率：10

输入费用：10

7 年后，投资翻了一番。

我已经制定了以下代码，但我收到一条关于 t 的错误消息。 如果我能得到一些帮助，我将不胜感激，谢谢！：

t=0
p=float(input("Enter the investment:"))

a=float(input("Enter the interest rate:"))

m=float(input("Enter the fee:"))

i=(float(a/100))
f=p
while f<=(2*p):
    f=(float(f*((1+i)**t)-m)
    t=t+1

print("The investment doubles after",t,"years")

Answer 1

我试图以一种非常容易理解和理解的方式来写这篇文章。 我用注释对其进行了编辑，以逐行解释正在发生的事情。 我建议使用更多的描述性变量。 t/p/a/m/f 对你来说可能很有意义，但是从现在起 6 个月后回到这个程序，你可能会在试图理解你想要完成的事情时遇到问题。 注意如果使用 Python 3+，您应该在我的示例中使用 input 而不是 raw_input 。 我使用 2.7，所以我使用 raw_input。

#first we define our main function
def main():
    #investment is a variable equal to user input. it is converted to a float so that the user may enter numbers with decimal places for cents
    investment = float(raw_input("Starting Investment:  "))
    #interest is the variable for interest rate. it is entered as a percentage so 5.5 would equate to 5.5%
    interest = float(raw_input("Interest Rate as %, ex: 5.5  "))
    #annual_fee is a variable that will hold the value for the annual fee.
    annual_fee = float(raw_input("Annual Fee:  "))
    #years is a variable that we will use with a while loop, adding 1 to each year (but we wait until within the loop to do this)
    years = 1
    #we use a while loop as opposed to a for loop because we do not know how many times we will have to iterate through this loop to achieve a result. while true is always true, so this segment is going to run without conditions
    while True:
        #this is a variable that holds the value of our total money per year, this is equal to the initial investment + investment * interest percentage - our annual fee per year
        #I actually had to try a few different things to get this to work, a regular expression may have been more suited to achieve an interest % that would be easier to work with. do some research on regular expressions in python as you will sooner or later need it.
        total_per_year = investment + (years * (investment * (interest / 100))) - (annual_fee * years)
        #now we start adding 1 to our years variable, since this is a while loop, this will recalculate the value of total_per_year variable
        years += 1
        #the conditional statement for when our total_per_year becomes equal to double our initial investment
        if total_per_year >= 2 * investment:
            #print years value (at time condition is met, so it will be 5 if it takes 5 years) and the string ' Years to Double Investment'
            print years,' Years to Double Investment'
            #prints 'You will have $' string and then the value our variable total_per_year
            print 'You will have $', total_per_year
            #this will break our while loop so that it does not run endlessly
            break
        #here is error handling for if the fee is larger than investment + interest
        if (years * annual_fee) >= (years * (investment * (interest / 100))):
            print('Annual Fee Exceeds Interest - Losing Money')
            break
#initial call of our main function/begins loop
main()