Python Version of Homework #3

[nemorathwald]

# Finds out how many months it takes to pay off a $1000 purchase with no downpayment.

rate = .015 # Interest rate of 1.5% per month.
payment = 50 # Monthly payment.
balance = 1000 # How much debt remains.
months = 0 # How many monthly payments have been made so far.

while balance > 0:
  thismonthsinterest = balance * rate # How much debt accrues this month
  balance = balance + thismonthsinterest - payment
  months += 1
  print months, ' Interest: $%.2f' % thismonthsinterest, ' Balance: $%.2f' % balance

This gives the output:

1  Interest: $15.00  Balance: $965.00
2  Interest: $14.47  Balance: $929.48
3  Interest: $13.94  Balance: $893.42
4  Interest: $13.40  Balance: $856.82
5  Interest: $12.85  Balance: $819.67
6  Interest: $12.30  Balance: $781.97
7  Interest: $11.73  Balance: $743.70
8  Interest: $11.16  Balance: $704.85
9  Interest: $10.57  Balance: $665.42
10  Interest: $9.98  Balance: $625.40
11  Interest: $9.38  Balance: $584.79
12  Interest: $8.77  Balance: $543.56
13  Interest: $8.15  Balance: $501.71
14  Interest: $7.53  Balance: $459.24
15  Interest: $6.89  Balance: $416.13
16  Interest: $6.24  Balance: $372.37
17  Interest: $5.59  Balance: $327.95
18  Interest: $4.92  Balance: $282.87
19  Interest: $4.24  Balance: $237.11
20  Interest: $3.56  Balance: $190.67
21  Interest: $2.86  Balance: $143.53
22  Interest: $2.15  Balance: $95.68
23  Interest: $1.44  Balance: $47.12
24  Interest: $0.71  Balance: $-2.17

Comments

[crywolf.livejournal.com]

Slight bug there at the end. It's not difficult to fix, though, and I'm guessing you've already seen it.

[matt-arnold.livejournal.com]

Are you talking about the negative balance? I don't see that as a problem.

[crywolf.livejournal.com]

I'd consider it a problem, since balanced owed generally shouldn't be able to go negative. I suppose it depends on the scope of the assignment, although the last paragraph of the description seems to indicate that the last payment should be smaller: "The last payment may be less that $50 if the debt is small, but do not forget the interest." I suppose it all depends on the definition of "may".

[arran4.livejournal.com]

Perhaps it has uses to know exactly how much was required to pay it off on the last payment?