Question

The problem is to write the python that calculates the interest due on a loan and prints a payment schedule. The interest due on a loan can be calculated according to the simple formula:

I = P × R × T

where I is the interest paid, P is the amount borrowed (principal), R is the interest rate, and T is the length of the loan.

Finally it needs to displayed as follows:

The program will print the amount borrowed, total interest paid, the amount of the monthly payment, and a payment schedule.

Sample session

Loan calculator

Amount borrowed: 100
Interest rate: 6
Term (years): 1

Amount borrowed:    $100.00
Total interest paid:  $6.00

           Amount     Remaining
Pymt#       Paid       Balance
-----      -------    ---------
  0        $ 0.00      $106.00
  1        $ 8.84      $ 97.16
  2        $ 8.84      $ 88.32
  3        $ 8.84      $ 79.48
  4        $ 8.84      $ 70.64
  5        $ 8.84      $ 61.80
  6        $ 8.84      $ 52.96
  7        $ 8.84      $ 44.12
  8        $ 8.84      $ 35.28
  9        $ 8.84      $ 26.44
 10        $ 8.84      $ 17.60
 11        $ 8.84      $  8.76
 12        $ 8.76      $  0.00

The complete problem description is here: http://openbookproject.net/pybiblio/practice/wilson/loan.php
To accomplish this I have written the code which is as follows:

import decimal
from decimal import *
class loan_calc:

 def __init__(self):
  decimal.getcontext().prec = 3
  p = Decimal(input('Please enter your loan amount:'))
  r = Decimal(input('Please enter the rate of interest:'))
  t = Decimal(input('Please enter loan period:'))
  r_e = r/100
  i = p*r_e*t 
  term = t*12
  r_a = p+i
  amnt = p/term
  count = 0
  b_r = r_a
  print "Payment\t\tAmount Paid\t\tBal.Rem."
  while count <= term:
   if count == 0:
    print count,"\t\t"'0.00'"\t\t\t",b_r
    count += 1
    b_r -= amnt
    continue

   if term - count == 1:
    amnt = b_r
    print count,"\t\t",amnt,"\t\t\t",b_r
    count += 1
    b_r -= amnt
    continue

   else: 
    print count,"\t\t",amnt,"\t\t\t",b_r
    b_r -= amnt
    count += 1
    continue



loan = loan_calc()

Answer 1

Here’s an answer closely patterned to the way yours is written. Using the method I explained and suggested when you asked about how to round off a floating number in python, it uses the decimal module equivalent of the math module’s ceil function to get the same answer as shown at the practice link (except for some minor output formatting). I also re-indented the code to the more commonly used 4-spaces, and renamed the variables to be a little more readable. Hope you learn something from it. Notice that I don’t set decimal.getcontext().prec to 3 (I don’t believe it does what you think).

import decimal

def main():
    principle = decimal.Decimal(raw_input('Please enter your loan amount:'))
    rate = decimal.Decimal(raw_input('Please enter rate of interest (percent):')) / 100
    term = decimal.Decimal(raw_input('Please enter loan period (years):')) * 12

    interest = (principle * rate).quantize(decimal.Decimal('.01'), rounding=decimal.ROUND_HALF_EVEN)
    balance = principle + interest
    payment = (balance / term).quantize(decimal.Decimal('.01'), rounding=decimal.ROUND_CEILING)
    print "Payment\t\tAmount Paid\t\tRem.Bal."
    for count in range(1+term):
        if count == 0:
            print count, "\t\t0.00\t\t\t", balance
        elif count == term: # last payment?
            payment = balance
            balance -= payment
            print count, "\t\t", payment, "\t\t\t", balance
        else:
            balance -= payment
            print count, "\t\t", payment, "\t\t\t", balance

main()

# > python loan_calc.py
# Please enter your loan amount:100
# Please enter rate of interest (percent):6
# Please enter loan period (years):1
# Payment         Amount Paid             Rem.Bal.
# 0               0.00                    106.00
# 1               8.84                    97.16
# 2               8.84                    88.32
# 3               8.84                    79.48
# 4               8.84                    70.64
# 5               8.84                    61.80
# 6               8.84                    52.96
# 7               8.84                    44.12
# 8               8.84                    35.28
# 9               8.84                    26.44
# 10              8.84                    17.60
# 11              8.84                    8.76
# 12              8.76                    0.00