merge branch publish

Makefile

@@ -3,5 +3,5 @@ reference:
 	amortize -P 100000 -r 0.05 -f monthly -n 36 -s > ref.txt
 
 test:
-	python amort.py -p 100000 -i 5.0 -t 3 -ot "{\"payment_number\":13,\"amount\":5000}"
+	python src/amort.py -p 100000 -i 5.0 -t 3 -ot "{\"payment-number\":13,\"amount\":5000}"
 

README.md

@@ -0,0 +1,45 @@
+
+# amort
+
+Generates an amortization schedule based on the principal, interest rate, term, and any additional payments towards principal.
+
+## requirements
+
+Only imports `argparse` and `json` for the main block of the script.
+
+* saves results to a file `schedule.csv`
+* does not access the web or internet
+
+## usage
+
+Invoke `make test` to generate a schedule based on loan of 100,000 over a 3 year term given an interest rate of 5.0% with a one-time payment towards principal of 5000 at the 13th month.
+
+### extra payments
+
+For extra payments towards principal, invoking the script will look like:
+
+    python src/amort.py -p {principal} -i {interest rate} -t {years} --extra-payments extra_payments.json
+
+A valid json file contains a list named `extra-payments`. Each element is an object with the attributes `payment-number` and `amount`.
+
+    {
+        "extra-payments" : [
+            {
+                "payment-number": 1,
+                "amount": 500
+            }, {
+                "payment-number": 2,
+                "amount": 500
+            }, {
+                "payment-number": 3,
+                "amount": 500
+            }
+        ]
+    }
+
+* `payment-number` is the month when the payment has been made.
+* `amount` is self-explanatory
+
+## misc
+
+This originated from me playing with ChatGPT. I asked it a question and it blurted out a semi-functional script as an answer. Then I made this repo to track the errors I fixed.

src/amort.py

@@ -1,6 +1,4 @@
 
-import argparse, json
-
 def generate_amortization_schedule(principal, interest_rate, loan_term, extra_payments=[]):
     # Convert interest rate to decimal and calculate periodic interest rate
     monthly_interest_rate = interest_rate / 12 / 100
@@ -29,7 +27,7 @@ def generate_amortization_schedule(principal, interest_rate, loan_term, extra_pa
         principal_payment = round(monthly_payment - interest_payment, 2)
 
         # Apply one-time payment if provided
-        if one_time_payment and payment_number == one_time_payment['payment_number']:
+        if one_time_payment and payment_number == one_time_payment['payment-number']:
             principal_payment += one_time_payment['amount']
             if extra_payments != []:
                 one_time_payment = extra_payments.pop(0)
@@ -72,7 +70,30 @@ def get_totals(amortization_schedule, func=None):
         func(messages)
     return total_paid, total_interest_paid, total_principal_paid
 
+def compare(with_extra_payments, without):
+    x,y,z = get_totals(with_extra_payments)
+    a,b,c = get_totals(without)
+    term_length = len(without) - len(with_extra_payments)
+    print(chr(916), "paid: ", round(x-a,2))
+    print(chr(916), "interest paid: ", round(y-b,2))
+    print(chr(916), "principal paid: ", round(abs(z-c),2))
+    print(chr(916), "term (months): ", term_length)
+
+def display(table):
+    print("id, paid, interest payment, principal payment, remaining")
+    for row in table:
+        print(row)
+
+def export(table, filename="schedule.csv"):
+    with open(filename, 'w') as f:
+        print("id, paid, interest payment, principal payment, remaining", file=f)
+        for row in table:
+            print(row, file=f)
+    print("wrote to file", filename)
+
 if __name__ == "__main__":
+    import argparse, json
+
     def get_arguments():
         p = argparse.ArgumentParser()
         p. add_argument("--principal", "-p", type=float, \
@@ -82,7 +103,7 @@ if __name__ == "__main__":
         p.add_argument("--term", "-t", type=int,\
             help="sets the term (years)")
         p.add_argument("--one-time", "-ot", type=str,\
-            help="factors in a one-time payment (json, example: {\"payment_number\":13,\"amount\":5000}")
+            help="factors in a one-time payment (json, example: {\"payment-number\":13,\"amount\":5000}")
         p.add_argument("--extra-payments", "-ep", type=str,\
             help="facts in multiple one time payments (json file name)")
         args = p.parse_args()
@@ -90,32 +111,14 @@ if __name__ == "__main__":
         if args.extra_payments is not None:
             with open(args.extra_payments) as f:
                 l = json.loads(f.read())
-                # print(extra["extra-payments"])
-        if args.one_time is not None:
-            l.append(json.loads(args.one_time))
+        extra = []
+        if "extra-payments" in l:
             extra = l["extra-payments"]
-        extra.sort(key=lambda k: k["payment_number"])
+            extra.sort(key=lambda k: k["payment-number"])
+        if args.one_time is not None:
+            extra.append(json.loads(args.one_time))
         return args.principal, args.interest_rate, args.term, extra
 
-    def compare(with_extra_payments, without):
-        x,y,z = get_totals(with_extra_payments)
-        a,b,c = get_totals(without)
-        print(chr(916), "paid: ", round(x-a,2))
-        print(chr(916), "interest paid: ", round(y-b,2))
-        print(chr(916), "principal paid: ", round(abs(z-c),2))
-
-    def display(table):
-        print("id, paid, interest payment, principal payment, remaining")
-        for row in table:
-            print(row)
-
-    def export(table, filename="schedule.csv"):
-        with open(filename, 'w') as f:
-            print("id, paid, interest payment, principal payment, remaining", file=f)
-            for row in table:
-                print(row, file=f)
-        print("wrote to file", filename)
-
     principal, interest_rate, loan_term, extra_payments = get_arguments()
 
     schedule = generate_amortization_schedule(principal, interest_rate, loan_term, extra_payments)