贷款计算器的 Python 编码问题

Question

I am trying to create a loan calculator on a website and I am getting trouble in the coding of Python. The code is:

# user enter the cost of the loan, the interest rate, and
#the number of years for the loan
#Calculate monthly payments with the following formula
# M = L[i(1+i)n] / [(1+i)n-2]
# M = monthly payment
# L = Loan amount
# i = interest rate (for an interest rate of 5%, i = 0.05)
# n = number of payments
#________________________________________________________________________#
#Start of program
#Declare variables

monthlypayment = 0  
loanamount = 0
interestrate = 0
numberofpayments = 0  
loandurationinyears = 0
loanamount = raw_input("Lending Money ")
interestrate = raw_input("Interest Rates are? ")
loandurationinyears = raw_input("Time Duration in Years?")
#Convert the strings into floating numbers so we can use them in the formula
loandurationinyears = float(loandurationinyears)
loanamount = float(loanamount)
interestrate = float(interestrate)
#Since payments are once per month, number of payments is number of years for the loan
payments = loaninyears*12
#calculate the monthly payment based on the formula
payment = amount * interestrate * (7+ interestrate) * payments / ((1 + interestrate) * payments -1)
#Result to the program
print("Payment will be " + st(monthlypayment))

Can any experienced person help me to get the syntax or other logical errors in this coding?

Answer 1

You are reading variables that you have not previously declared. Change loaninyears to loandurationinyears and amount to loanamount .

Additionally you have a typo in the last line, st should be str

Also some tips:

First, you can do stuff like:

input = float(raw_input("Give me some number"))

This way you can shorten the length of your program.

Also you might want to consider using a more readable variable naming, for example:

loanInYears or loan_in_years

Answer 2

Following your formula in the comments closely, and using Python 2.7 , this runs, but the outcome isn't correct.

# user enter the cost of the loan, the interest rate, and
#the number of years for the loan
#Calculate monthly payments with the following formula
# M = monthly payment
# L = Loan amount
# i = interest rate (for an interest rate of 5%, i = 0.05)
# n = number of payments

L = input ('loan amount')
i = input ('interest rate')
n = input ('nr of payments')

M = L*(i*(1+i)*n) / ((1+i)*n-2)

print (M)

I think you should fix your formula first, apart from coding errors. Specifically I miss the number 12 somewhere, since your interest is per year, but your payments are per month.

[EDIT]

Look at the answer of Joshy here:

Formula for calculating interest Python

and perhaps use a different video tutorial, since this one seems to get many folks in trouble.

Tip: ifyouhaveverylongvariablenames you_may_place_some_underscores_in_them