At this state, it produces a nice web-based viewer of the loan files including the payment history and future amortization.

web.py

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+from flask import Flask, render_template, request, redirect, url_for
+import json
+from decimal import *
+from datetime import *
+from jinja2 import Environment, FileSystemLoader
+from fpdf import FPDF, HTMLMixin
+import smtplib
+
+from email.MIMEMultipart import MIMEMultipart
+from email.MIMEText import MIMEText
+from email.MIMEBase import MIMEBase
+from email import Encoders
+
+app = Flask(__name__)
+
+@app.route('/')
+def hello():
+
+    loans = []
+    loans.append( addLoan("1 Greenfield Lane Mortgage", "greenfield_mortgage.json" ) )
+    loans.append( addLoan("2 Bear Houses LLC Loan", "9Kloan.json" ) )
+    loans.append( addLoan("3 Brenda Mortgage", "brendamortgage.json" ) )
+    loans.append( addLoan("4 Dad Mortgage", "dadmortgage.json") )
+
+    if 'loan' in request.args:
+        filename = request.args["loan"]
+    else:
+        return redirect('/?loan=' + loans[0]['filename'])
+
+    loan = loadLoanInformation('/Users/john/PycharmProjects/mortgage/' + filename)
+    amortizeLoan(loan)
+
+    return render_template('main.html', filename=filename, loans=loans, model=loan)
+
+@app.route('/update_file')
+def update_file():
+    return
+
+@app.route('/send_statement', methods=['POST'])
+def send_statement():
+    loan = request.form["loan"]
+    redirect( '/?loan=' + loan )
+
+def addLoan(loanName, fileName):
+    x = {}
+    x['name'] = loanName
+    x['filename'] = fileName
+    return x
+
+'''from old code'''
+def getStatementHeader(datastore):
+    return datastore['header']
+
+
+def getEmailInformation(datastore):
+    return datastore['email']
+
+
+def loadLoanInformation(filename):
+    datastore = getDatastore(filename)
+
+    loanModel = {}
+    loanModel['datastore'] = datastore
+    loanModel['email'] = getEmailInformation(datastore)
+    loanModel['parameters'] = getLoanParameters(datastore)
+    loanModel['lender'] = getLender(datastore)
+    loanModel['borrower'] = getBorrower(datastore)
+    loanModel['header'] = getStatementHeader(datastore)
+    return loanModel
+
+
+def getLoanParameters(datastore):
+    # read in the loan profile information
+    loan = datastore['parameters']
+
+    annual_rate = Decimal(loan['interest_rate']) / 100
+    daily_interest_rate = annual_rate / 360
+    principal = Decimal(loan["principal"]).quantize(Decimal("1.00"))
+    periods_per_year = Decimal(loan["periods_per_year"])
+    total_periods = Decimal(loan["periods"])
+    payment_day_of_month = int(loan['payment_day_of_month'])
+
+    if "monthly_payment" in loan:
+        monthly_payment = Decimal(loan["monthly_payment"]).quantize(Decimal("1.00"))
+    else:
+        # calculate expected monthly payment
+        periodic_rate = annual_rate / periods_per_year
+        discount_factor = (((1 + periodic_rate) ** total_periods) - 1) / (
+                periodic_rate * ((1 + periodic_rate) ** total_periods))
+        monthly_payment = (principal / discount_factor).quantize(Decimal("1.00"))
+
+    loan['principal'] = principal       # standardizes the format
+    loan['annual_rate'] = annual_rate   # standardizes the format
+    loan['daily_interest_rate'] = daily_interest_rate
+    loan['rate'] = '' + (annual_rate * 100).__str__() + '%'
+    loan['next_payment_amt'] = 0
+    loan['next_payment_date'] = '12/12/12'
+    loan['total_periods'] = total_periods
+    loan['monthly_payment'] = monthly_payment
+    datastore['parameters'] = loan
+    return loan
+
+
+def getLender(datastore):
+    return datastore['lender']
+
+
+def getBorrower(datastore):
+    return datastore['borrower']
+
+
+def getDatastore(filename=None):
+    try:
+        if filename:
+            with open(filename, 'r') as f:
+                datastore = json.load(f)
+
+    except Exception as e:
+        print "An error occurred opening your loan file '%s'. " % filename
+        print "The Exception:"
+        print e.__repr__()
+        quit()
+
+    return datastore
+
+
+def amortizeLoan(loan):
+    # loop over the payments and calculate the actual amortization
+    monthly_payment = loan["parameters"]["monthly_payment"]
+
+    actual_payments = loan["datastore"]["payments"]
+
+    remaining_principal = loan["parameters"]["principal"]
+    payment_day_of_month = int(loan["parameters"]["payment_day_of_month"])
+    daily_interest_rate = loan["parameters"]["daily_interest_rate"]
+    total_periods = loan["parameters"]["total_periods"]
+    interest_paid_through_date = datetime.strptime(loan["parameters"]["start_interest_date"], "%Y-%m-%d").date()
+    next_payment_date = datetime.strptime(loan["parameters"]["first_payment_month"], '%Y-%m-%d').date()
+    next_bill_date = date(year=next_payment_date.year, month=next_payment_date.month, day=payment_day_of_month)
+
+    payment_number = 1
+    annual_interest = 0
+    total_interest = 0
+    old_bill_date = next_bill_date
+    current_year = next_bill_date.year
+
+    past_payments = []
+    future_payments = []
+
+    for payment in actual_payments:
+        payment_date = datetime.strptime((payment[0]), '%Y-%m-%d').date()
+        payment_amount = Decimal(payment[1]).quantize(Decimal("1.00"))
+        days_since_last_payment = (payment_date - interest_paid_through_date).days
+
+        #check for out of order payments, generally a sign of a data entry problem, especially years
+        if days_since_last_payment < 0:
+            print "Payment Number %s appears out of order.  The payment date '%s' is before the previous payment on '%s'." \
+                  % (payment_number, payment_date, interest_paid_through_date)
+            quit()
+
+        new_interest = (days_since_last_payment * remaining_principal * daily_interest_rate).quantize(Decimal("0.00"))
+        new_principal = payment_amount - new_interest
+        interest_paid_through_date = payment_date
+        total_interest = total_interest + new_interest
+        annual_interest = annual_interest + new_interest
+        remaining_principal = remaining_principal - new_principal
+
+
+        # create the payment record for the template to render
+        payment_record = {}
+        payment_record['year']=next_bill_date.year
+        payment_record['month']=next_bill_date.month
+        payment_record['payment_number'] = payment_number
+        payment_record['bill_date'] = next_bill_date
+        payment_record['payment_date'] = payment_date
+        payment_record['days_of_interest'] = days_since_last_payment
+        payment_record['payment_amount'] = payment_amount
+        payment_record['principal_payment'] = payment_amount - new_interest
+        payment_record['interest_payment'] = new_interest
+        payment_record['new_balance'] = remaining_principal
+        payment_record['interest_to_date'] = total_interest
+        payment_record['annual_interest_to_date'] = annual_interest
+        past_payments.append(payment_record)
+
+        payment_number = payment_number + 1
+        old_bill_date = next_bill_date
+
+        if old_bill_date.month < 12:
+            next_bill_date = date(year=old_bill_date.year, month=old_bill_date.month + 1, day=payment_day_of_month)
+        else:
+            annual_interest = Decimal("0.00")
+            next_bill_date = date(year=old_bill_date.year + 1, month=1, day = payment_day_of_month)
+
+    loan["total_interest_paid_to_date"] = total_interest
+    loan["parameters"]["next_due_date"] = next_bill_date
+
+    if (remaining_principal < monthly_payment):
+        loan["parameters"]["next_payment_amt"] = remaining_principal
+    else:
+        loan["parameters"]["next_payment_amt"] = monthly_payment
+
+    # loop over remaining scheduled payments and present estimated amortization
+    while (payment_number <= total_periods) and (remaining_principal > 0):
+        days_since_last_payment = (next_bill_date - interest_paid_through_date).days
+        new_interest = (days_since_last_payment * remaining_principal * daily_interest_rate).quantize(Decimal("0.00"))
+
+        # make sure the last payment isn't too much
+        if new_interest + remaining_principal < monthly_payment:
+            monthly_payment = new_interest + remaining_principal
+
+        new_principal = monthly_payment - new_interest
+
+        remaining_principal = remaining_principal - new_principal
+
+        interest_paid_through_date = next_bill_date
+
+        # complete the future payment amortization record
+        future_payment_record = {}
+        future_payment_record['payment_number'] = payment_number
+        future_payment_record['payment_date'] = next_bill_date
+        future_payment_record['days_of_interest'] = days_since_last_payment
+        future_payment_record['payment_amount'] = monthly_payment
+        future_payment_record['principal_payment'] = new_principal
+        future_payment_record['interest_payment'] = new_interest
+        future_payment_record['new_balance'] = remaining_principal
+        future_payments.append(future_payment_record)
+
+        payment_number = payment_number + 1
+        old_bill_date = next_bill_date
+        if old_bill_date.month < 12:
+            next_bill_date = date(year=old_bill_date.year, month=old_bill_date.month + 1, day=payment_day_of_month)
+        else:
+            next_bill_date = date(year=old_bill_date.year + 1, month=1, day=payment_day_of_month)
+
+
+    loan["balloon_payment"] = remaining_principal
+    loan["past_payments"] = past_payments
+    loan["future_payments"] = future_payments
+    return
+
+
+if __name__ == '__main__':
+    app.debug = True
+    app.run()