Loan Calculator

Calculation of differentiated payments. To do this, the user can run the program specifying interest, number of monthly payments, and loan principal. Ability to calculate the same values as in the previous stage for annuity payment (principal, number of monthly payments, and monthly payment amount). The user specifies all the known parameters with command-line arguments, and one parameter will be unknown. This is the value the user wants to calculate. Handling of invalid parameters. It's a good idea to show an error message if the user enters invalid parameters (they are discussed in detail below). The final version of your program is supposed to work from the command line and parse the following parameters:

--type indicates the type of payment: "annuity" or "diff" (differentiated). If --type is specified neither as "annuity" nor as "diff" or not specified at all, show the error message.

python creditcalc.py --principal=1000000 --periods=60 --interest=10 Incorrect parameters --payment is the monthly payment amount. For --type=diff, the payment is different each month, so we can't calculate months or principal, therefore a combination with --payment is invalid, too: python creditcalc.py --type=diff --principal=1000000 --interest=10 --payment=100000 Incorrect parameters --principal is used for calculations of both types of payment. You can get its value if you know the interest, annuity payment, and number of months. --periods denotes the number of months needed to repay the loan. It's calculated based on the interest, annuity payment, and principal. --interest is specified without a percent sign. Note that it can accept a floating-point value. Our loan calculator can't calculate the interest, so it must always be provided. These parameters are incorrect because --interest is missing: python creditcalc.py --type=annuity --principal=100000 --payment=10400 --periods=8 Incorrect parameters You may have noticed that for differentiated payments you will need 4 out of 5 parameters (excluding payment), and the same is true for annuity payments (the user will be calculating the number of payments, the payment amount, or the loan principal). Thus, you should also display an error message when fewer than four parameters are provided:

python creditcalc.py --type=annuity --principal=1000000 --payment=104000 Incorrect parameters You should also display an error message when negative values are entered:

python creditcalc.py --type=diff --principal=30000 --periods=-14 --interest=10 Incorrect parameters The only thing left is to compute the overpayment: the amount of interest paid over the whole term of the loan. Voila: you have a real loan calculator!

Examples The greater-than symbol followed by a space (> ) represents the user input. Note that this is not part of the input.

Example 1: calculating differentiated payments

python creditcalc.py --type=diff --principal=1000000 --periods=10 --interest=10 Month 1: payment is 108334 Month 2: payment is 107500 Month 3: payment is 106667 Month 4: payment is 105834 Month 5: payment is 105000 Month 6: payment is 104167 Month 7: payment is 103334 Month 8: payment is 102500 Month 9: payment is 101667 Month 10: payment is 100834

Overpayment = 45837 In this example, the user wants to take a loan with differentiated payments. You know the principal, the count of periods, and interest, which are 1,000,000, 10 months, and 10%, respectively.

Finally, your loan calculator should add up all the payments and subtract the loan principal so that you get the overpayment.

Example 2: calculate the annuity payment for a 60-month (5-year) loan with a principal amount of 1,000,000 at 10% interest

python creditcalc.py --type=annuity --principal=1000000 --periods=60 --interest=10 Your annuity payment = 21248! Overpayment = 274880 Example 3: fewer than four arguments are given

python creditcalc.py --type=diff --principal=1000000 --payment=104000 Incorrect parameters. Example 4: calculate differentiated payments given a principal of 500,000 over 8 months at an interest rate of 7.8%

python creditcalc.py --type=diff --principal=500000 --periods=8 --interest=7.8 Month 1: payment is 65750 Month 2: payment is 65344 Month 3: payment is 64938 Month 4: payment is 64532 Month 5: payment is 64125 Month 6: payment is 63719 Month 7: payment is 63313 Month 8: payment is 62907

Overpayment = 14628 Example 5: calculate the principal for a user paying 8,722 per month for 120 months (10 years) at 5.6% interest

python creditcalc.py --type=annuity --payment=8722 --periods=120 --interest=5.6 Your loan principal = 800018! Overpayment = 246622 Example 6: calculate how long it will take to repay a loan with 500,000 principal, monthly payment of 23,000, and 7.8% interest

python creditcalc.py --type=annuity --principal=500000 --payment=23000 --interest=7.8 It will take 2 years to repay this loan! Overpayment = 52000

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