我目前正在通过youtube上的视频教程来学习python，并且遇到了一个我似乎无法掌握的公式，因为对我而言，没有任何东西适合我。练习的基本概念是制作一个抵押计算器，要求用户输入3条信息，即贷款金额，利率和贷款期限(年)。
然后计算向用户支付的每月费用。这是我的代码:
__author__ = 'Rick'
# This program calculates monthly repayments on an interest rate loan/mortgage.
loanAmount = input("How much do you want to borrow? \n")
interestRate = input("What is the interest rate on your loan? \n")
repaymentLength = input("How many years to repay your loan? \n")
#converting the string input variables to float
loanAmount = float(loanAmount)
interestRate = float(interestRate)
repaymentLength = float(repaymentLength)
#working out the interest rate to a decimal number
interestCalculation = interestRate / 100
print(interestRate)
print(interestCalculation)
#working out the number of payments over the course of the loan period.
numberOfPayments = repaymentLength*12
#Formula
#M = L[i(1+i)n] / [(1+i)n-1]
# * M = Monthly Payment (what were trying to find out)
# * L = Loan Amount (loanAmount)
# * I = Interest Rate (for an interest rate of 5%, i = 0.05 (interestCalculation)
# * N = Number of Payments (repaymentLength)
monthlyRepaymentCost = loanAmount * interestCalculation * (1+interestCalculation) * numberOfPayments / ((1+interestCalculation) * numberOfPayments - 1)
#THIS IS FROM ANOTHER BIT OF CODE THAT IS SUPPOSE TO BE RIGHT BUT ISNT---
# repaymentCost = loanAmount * interestRate * (1+ interestRate) * numberOfPayments / ((1 + interestRate) * numberOfPayments -1)
#working out the total cost of the repayment over the full term of the loan
totalCharge = (monthlyRepaymentCost * numberOfPayments) - loanAmount
print("You want to borrow £" + str(loanAmount) + " over " + str(repaymentLength) + " years, with an interest rate of " + str(interestRate) + "%!")
print("Your monthly repayment will be £" + str(monthlyRepaymentCost))
print("Your monthly repayment will be £%.2f " % monthlyRepaymentCost)
print("The total charge on this loan will be £%.2f !" % totalCharge)
一切正常，但是最后抛出的值(value)是完全错误的……一笔100英镑的贷款，一年期利率为10％，不应该让我每月支付0.83英镑。我们将不胜感激，帮助我绕开这个方程式以帮助我理解。
最佳答案
借助示例，这就是我所做的。
# Formula for mortgage calculator
# M = L(I(1 + I)**N) / ((1 + I)**N - 1)
# M = Monthly Payment, L = Loan, I = Interest, N = Number of payments, ** = exponent
# Declares and asks for user to input loan amount. Then converts to float
loanAmount = input('Enter loan amount \n')
loanAmount = float(loanAmount)
# Declares and asks user to input number of payments in years. Then converts to float. Years * 12 to get
# total number of months
years = input('How many years will you have the loan? \n')
years = float(years) * 12
# Declares and asks user to input interest rate. Then converts to float and input interest rate is /100/12
interestRate = input('Enter Interest Rate \n')
interestRate = float(interestRate) / 100 / 12
# Formula to calculate monthly payments
mortgagePayment = loanAmount * (interestRate * (1 + interestRate)
** years) / ((1 + interestRate) ** years - 1)
# Prints monthly payment on next line and reformat the string to a float using 2 decimal places
print("The monthly mortgage payment is\n (%.2f) " % mortgagePayment)