Question

CIS 221 Loan Calculator Enhancement

Introduction

You are a systems analyst working for a company that provides loans to customers. Your manager has asked you to enhance and correct their existing Loan Calculator program, which is designed to calculate monthly and total payments given the loan amount, the annual interest rate, and the duration of the loan. Although the current version of the program (hereby termed the “As Is” version) has some functionality, there are several missing pieces, and the user would like to see significant improvements. Also, the program has some bugs that need to be fixed. After a requirements elicitation session (see https://en.wikipedia.org/wiki/Requirements_elicitation), you have uncovered the following facts about the As Is version, and you are prepared to work with this existing program and create the enhanced version (hereby termed the To Be version).

Note: the as-is program is Listing 9.11 LoanCalculator.py, which is described in section 9.7 of the textbook. The existing code is available in the Ch9 examples, which you can download from Canvas.

The requirements are discussed below.

The As Is System

In its current state, the program takes user input in the form of an annual interest rate, number of years, and total loan amount. It displays the calculated monthly payment, and the calculated total payment. This image shows an example.

This is fine as far as it goes. But it has a glitch. For example, if the user fails to enter proper numeric values, the program aborts with an ugly message like this:

Users are very annoyed when they see this, and they have to restart the program in order to continue their work.

Also, the program is incomplete. There is more functionality that the users want, which is described below.

The To Be System

The users would like additional functionality to the program, and also some corrections.

First, your program should handle exceptions more gracefully. Rather than the ugly situation described above, an error message should appear telling the user what correction to make. For example, if the user clicks the calculate button without having proper input data entered, you should display a dialog like this:

Second, the program should include an amortization schedule. This should be displayed in a Text widget. This screens shows an example of what would appear given user input:

Note also that the interest, monthly payment, and total payment values are shown in nice currency format. In order to make these amounts show up with good currency format, you can make use of Python’s locale module: https://docs.python.org/2/library/locale.html. Use Google to find out how you can do this.

Finally, we want to be able to save the loan report to a file (note the extra button in the above figure). If the user wants to do this, you should prompt the user to enter the loan recipient’s name using a dialog, as shown below:

When the user enters the name, you should write to a file named based on the entered name. This should include data shown as below:

In addition to the proper functioning program, please also include a modified UML diagram. The original UML diagram is included in the PowerPoints for Ch9. The modified UML diagram will include any additional methods you wrote to accomplish your programming task.

Final Deliverables:

Upload the modified Python program and the modified UML diagram to Canvas.

Answer 1

Screenshot of the code:

#Import the required packages. from tkinter import* import tkinter.messagebox import tkinter. simpledialog #Define the class LoanCalculator. class LoanCalculator: #Define the constructor of the class. def _init (self): #create a window . window-Tk() # Create a window #set the title of the window window.title ("Loan Calculator") #set the orientation of window window.geometry)xt'.format (400, 150)) #create a label for the interest rate Label (window, text= "Annual Interest Rate").grid (row= 1, column= 1, sticky =W) #create a label for the number of years. Label (window, text- "Number of Years") .grid(row - 2, column - 1, sticky - W) #create a label for the loan amount. Label (window, text = "Loan Amount"). grid (row = 3, column= 1, sticky =W) #create a label for the monthly interest. Label (window, text - "Monthly Payment") .grid (row -4, column - 1, sticky-W) #create a label for the total payment. Label (window, text= "Total Payment").grid (row= 5, column = 1, sticky-W) #Prompt the user to enter the annual interest rate. self.ann int rate - StringVar () Entry (window, textvariable - self.ann int_rate, justify-RIGHT) .grid (row - 1, column - 2) #Prompt the user to enter the number of years. self.no of years StringVar () Entry (window, textvariable= self .noofyears, justify = RIGHT) .grid (row= 2, column= 2) - - #Prompt the user to enter the loan amount self.loan amt -StringVar () Entry (window, textvariable-self. loan amt, justify= RIGHT). grid (row = 3, column= 2) #Declare a label to store the monthly payment. self.monthly _pay - stringVar ) label mon pay-Label (window, textvariable-self . monthly pay), grid (row= 4, column= 2, sticky = E) #Declare a label to store the total payment self.tot_pay - Stringvar ) IblTotal Payment= Label (window, textvariable-self. tot pay). grid (row= 5, column= 2, sticky-E)

#Declare a button to calculate payment btn cal_pay - Button (window, text -"Compute Payment", command - self.caloulatepay) grid (row -7 , column - 1, stiaky - E) #Declare a button to load a file btn save file-Button (window, text -Save load to File", command-self.display Shedule) .grid(row - 7 , column -2, sticky - E) # Create a main loop window.nainloop() # Create an event loop Define the method calculate_pay ) def calculate pay (self): #Check if the interest rate , loan amount, number of years is not a digit, then show an error if (self.ann int rate.get) .replace(. ','',1).isdigitFalse or self.loan amt.get .replace(.','',1).isdigit ) False or self.no of_years.get .replace'.',',1) isdigito False): tkinter.messagebox.showerror ("Calculation Error", "Please make sure to enter numerio values for interest rate, years, and\nloan amount") return #store the returned value of the method get mon pay() into variable mon pay mon pay-self.get mon pay ( Eloat (self.loan amt.get ) float (self.ann int rate.get) 1200, int (self.no_of_years.get))) #set the monthly payment self.monthly pay.set (format (mon pay, '1.2f")) #Calculate the total payment surn pay float (self.monthly.pay.get()) * 12 \ * int (self.no_of_years.geto) #set the value of total payment variable self.tot pay.set (format (sum pay, '1-2f)) #Call the function amort sched() . self.amort Sched ( float (self.loan amt.geto), float (self.ann int rate.geto) / 1200. int (self.no_of_years.get())) Define the method display_shedule () def clisplay Shedule (self): #Check if the interest rate, loan amount, number of years is not a digit, then show an error. f self.ann_int rate.geto . replace('','',1).isdigitFalse or self. loan_amt.get .replace (".','',1).isdigit ) False or self. no of_years.get replace ('.','',1) .isdigito - False): tkinter.messagebox.showerror "Calculation Error", "Please make sure to enter numeric values for interest rate, years, and\nloan amount")

Prompt the user to enter the name of loan Recipient fname - tkinter.simpledialog.askstring ( "Loan Recipient ", "Enter the name of loan recipient") #Call the function printToFile() . self.printToFile (fname float (self.loanarnt.get)), float (self.ann_int rate.get 1200, int(self.no of years.get())) Define the method printToFile) def printToFile (self, fname, loan, mon int, num years): Append the loan document. txt with the name of the file fi Namefname+1oan document.txt" #Open the output file in write mode outfile - open (fi Name, 'w') store the header of the file headofFile -"ttt Loan Document for"+ fname "\n\tltt +Display the header to the file outfile.write (headofFile) #store the first line required fields of first -"\n\nLoan Amount: $, + line str (loan) "\tInterest Rate: str (self, ann-int rate .get()) "%\t\tNbr str (num years) "\n" + " + + Years: " + + Display the first line to the file outfile.write (first line) #Get the second line of the file sec line= "Monthly Payment; S" + str (self.monthly pay . get()) + "\t\tTotal Payment: $" + str (self, tot_pay.get()) + "\n" #Display the line to the file. outfile.write (sec line) Get the thíline third line ="\n\nAmortization schedule\npnt#\t\tínteres t\t\tprin pmt\t\tremi aning prin\n" - +Display this line to the file outfile.write (thi line) 择start a for loop till num-years+12 + 1 for i in range (1, num years12 1) Get the interest rate by multiplying monthly interest by loan amount and 10 and divide by 10 int rateint (mon int * loan 10) 10.0

tGet the principal amount by subtracting interest rate from monthly interest and multiply and divide the value by 10 pri_amt - int((float (self.monthly_pay.get-int_rate) * 10) / 10.0 Get the loan amount loan-int( (loanpri amt) 10) 10.0 #Get the resulted line res - (str+"tt\ts" + str(int rate)titits"str (pri amt)"titit\ts" + str (loan) "In") #write the resulted line to the file outfile.write (res) #close the file outfile.close () #Define the method amort sched() . def amort Sched (self, amt loan, month int rate, num vears): #create another window window - Tk () Set the title of the window window.title ("Amortization Schedule") #Add text to the window. txt-Text (window) Create and add text to the window txt.pack () #Declare the header line. line="\n\nAmortization schedule\n㏘t#1t\tínterest\t\tprin pmt\t\trenianing prinin" #insert this line into the text txt.insert (END, line) #start the for loop for i in range (1, num years* 12 + 1): #Get the value of interest rate int rate int (month int rate * art loan * 10) / 10.0 #Get the principal amount. prin_amt -int((float (self.monthly pay.getO) - int_rate) *10) / 10.0 Get the amount of the loan amt loan-int ((amt loan- prin amt)* 10) / 10.0 HGet the res-(str(i)"tlts" + str(int_rate) "tlt$" + str (prin amt) + "Itlts"str (amt_loan) + "In") #Insert the resulted value to the text. txt.insert (END, res) resulted value

#Define the method get mon pay() def get mon pay (self, loan, month int rate, num years): #Calculate the montly payment payofMonth -loan *month_int_rate / (1-1/ (1+month int rate)nm_years 12)) nuua payonwonth of monthly payment. return payofMonth; #call the Loancalculator() class to create the required GUI. LoanCalculator )

Sample Output:

Loan Calculator Annual Interest Rate Number of Years Loan Amount Monthly Payment Total Payment Compute PaymentSave load to File

Loan Calculator Annual Interest Rate Number of Years Loan Amount Monthly Payment Total Payment Compute PaymentSave load to File 8.5 100000 4545.57 109093.68

84520970901177800656 28670410913693726924 69084663686133933056 12445555432197429628 62840628406273950627 99888776665544333221 m2483-126199040880419 74197531087766556677 36914703681470369258 88899900001112222333 r3333334 444444444444 e3-724439466515775146 ee8-368023567899999987 t0852974-852963074185 n76665555444333322211 r# 01234567890

Loan Calculator Annual Interest Rate「 Number of Years 8.5 oan Amo Loan Recipient Monthly P Total Payr Enter the name of loan recipient Compute Alexander Cancel

Alexendarloan document.tt - Notepad File Edit Format View Help Loan Document for Alexendar Loan Amount : $100000.0 Interest Rate: 8.5% Monthly Payment: $4545.57 Nbr Years: 2 9 Total Payment: $109093.68 Amortization Schedule interest 3 remianing prin $708.3 $681.1 $653.7 $626.2 $598.4 $570.4 $96162.8 $92298.4 $88406.5 $84487..2 $80540.60 $76564.9 $72561.7 $68530.0 $64469.9 $60381.0 $56263.1 $52116.:1 $47939.7 $43733.17 $39497.8 $35232.0 $30936.0 $26609.6 $22252.5 $17864.6 $13445.6 $8995.3 $4513.4 $3837.2 $3864.4 $3891.8 $3919.3 $3947.1 $3975.1 $513.9 $4117.9 $4147.0 $4176.4 $4206.0 $4235.8 $4265.8 $4296.0 $4326.4 $4357.1 $4387.9 $398.5 $369.1 $339.5 $309.7 $279.7 $219.1 $%188.4 $157.6 $126.5 $4450.3 $4513.6

Code to copy:

#Import the required packages.

from tkinter import *

import tkinter.messagebox

import tkinter.simpledialog

#Define the class LoanCalculator.

class LoanCalculator:

#Define the constructor of the class.

def __init__(self):

     

    #Create a window.

    window = Tk() # Create a window

       

    #Set the title of the window.

    window.title("Loan Calculator") # Set title

     

    #Set the orientation of window.

    window.geometry('{}x{}'.format(400, 150))

   

    #Create a label for the interest rate.

    Label(window, text = "Annual Interest Rate").grid(row = 1, column = 1,sticky = W)

           

    #Create a label for the number of years.   

    Label(window, text = "Number of Years").grid(row = 2, column = 1, sticky = W)

           

    #Create a label for the loan amount.

    Label(window, text = "Loan Amount").grid(row = 3, column = 1, sticky = W)

           

    #Create a label for the monthly interest.   

    Label(window, text = "Monthly Payment").grid(row = 4, column = 1, sticky = W)

           

    #Create a label for the total payment.   

    Label(window, text = "Total Payment").grid(row = 5, column = 1, sticky = W)

     

    #Prompt the user to enter the annual interest rate.

    self.ann_int_rate = StringVar()

    Entry(window, textvariable = self.ann_int_rate, justify = RIGHT).grid(row = 1, column = 2)

    #Prompt the user to enter the number of years.

    self.no_of_years = StringVar()

    Entry(window, textvariable = self.no_of_years, justify = RIGHT).grid(row = 2, column = 2)

    #Prompt the user to enter the loan amount.

    self.loan_amt = StringVar()

    Entry(window, textvariable = self.loan_amt, justify = RIGHT).grid(row = 3, column = 2)

   

    #Declare a label to store the monthly payment.

    self.monthly_pay = StringVar()

    label_mon_pay = Label(window, textvariable = self.monthly_pay).grid(row = 4, column = 2, sticky = E)

   

    #Declare a label to store the total payment.

    self.tot_pay = StringVar()

    lblTotalPayment = Label(window, textvariable = self.tot_pay).grid(row = 5, column = 2, sticky = E)

   

    #Declare a button to calculate payment.

    btn_cal_pay = Button(window, text = "Compute Payment", command = self.calculate_pay).grid(row = 7 , column = 1, sticky = E)

   

    #Declare a button to load a file.

    btn_save_file = Button(window, text = "Save load to File", command = self.display_Shedule).grid(row = 7 , column = 2, sticky = E)

     

    # Create a main loop.

    window.mainloop() # Create an event loop

#Define the method calculate_pay().

def calculate_pay(self):

   

    #Check if the interest rate, loan amount, number of years is not a digit, then show an error.

    if (self.ann_int_rate.get().replace('.','',1).isdigit() == False

    or self.loan_amt.get().replace('.','',1).isdigit() == False

    or self.no_of_years.get().replace('.','',1).isdigit() == False):

      tkinter.messagebox.showerror("Calculation Error", "Please make sure to enter numeric values for interest rate, years, and\nloan amount")

    return

     

    #Store the returned value of the method get_mon_pay() into variable mon_pay.

    mon_pay = self.get_mon_pay(

    float(self.loan_amt.get()),

    float(self.ann_int_rate.get()) / 1200,

    int(self.no_of_years.get()))

     

    #Set the monthly payment.

    self.monthly_pay.set(format(mon_pay, '1.2f'))

     

    #Calculate the total payment.

    sum_pay = float(self.monthly_pay.get()) * 12 \

            * int(self.no_of_years.get())

     

    #Set the value of total payment variable.

    self.tot_pay.set(format(sum_pay, '1.2f'))

     

    #Call the function amort_Sched().

    self.amort_Sched(

    float(self.loan_amt.get()),

    float(self.ann_int_rate.get()) / 1200,

    int(self.no_of_years.get()))

#Define the method display_Shedule().

def display_Shedule(self):

   

    #Check if the interest rate, loan amount, number of years is not a digit, then show an error.

    if ( self.ann_int_rate.get().replace('.','',1).isdigit() == False

    or self.loan_amt.get().replace('.','',1).isdigit() == False

    or self.no_of_years.get().replace('.','',1).isdigit() == False):

      tkinter.messagebox.showerror("Calculation Error", "Please make sure to enter numeric values for interest rate, years, and\nloan amount")

   

    return

   

    #Prompt the user to enter the name of loan Recipient.

    fname = tkinter.simpledialog.askstring(

    "Loan Recipient ", "Enter the name of loan recipient")

   

    #Call the function printToFile().

    self.printToFile(fname,

    float(self.loan_amt.get()),

    float(self.ann_int_rate.get()) / 1200,

    int(self.no_of_years.get()))

#Define the method printToFile().

def printToFile(self,fname, loan, mon_int, num_years):

   

    #Append the loan document.txt with the name of the file.

    fi_Name = fname + "loan document.txt"

   

    #Open the output file in write mode.

    outfile = open(fi_Name, 'w')

   

    #Store the header of the file.

    headOfFile = "\t\t\t Loan Document for " + fname + "\n\t\t\t-------------------------------"

   

    #Display the header to the file.

    outfile.write(headOfFile)

   

    #Store the required fields of first line.

    first_line = "\n\nLoan Amount: $" + str(loan) + "\tInterest Rate: " + str(self.ann_int_rate.get()) + "%\t\tNbr Years: " + str(num_years) + "\n"

   

    #Display the first line to the file.

    outfile.write(first_line)

   

    #Get the second line of the file.

    sec_line = "Monthly Payment: $" + str(self.monthly_pay.get()) + "\t\tTotal Payment: $" + str(self.tot_pay.get()) + "\n"

   

    #Display the line to the file.

    outfile.write(sec_line)

   

    #Get the third line.

    thi_line = "\n\nAmortization    Schedule\npmt#\t\tinterest\t\tprin pmt\t\tremianing prin\n"

   

    #Display this line to the file.

    outfile.write(thi_line)

   

    #Start a for loop till num_years*12 + 1.

    for i in range(1, num_years * 12 + 1):

     

      #Get the interest rate by multiplying monthly interest by loan amount and 10 and divide by 10.

      int_rate = int(mon_int * loan * 10) / 10.0

     

      #Get the principal amount by subtracting interest rate from monthly interest and multiply and divide the value by 10.

      pri_amt = int((float(self.monthly_pay.get()) - int_rate) * 10) / 10.0

     

      #Get the loan amount.

      loan = int((loan - pri_amt) * 10) / 10.0

     

      #Get the resulted line.

      res = (str(i) + "\t\t\t$" + str(int_rate) + "\t\t\t$" + str(pri_amt) + "\t\t\t\t$" + str(loan) + "\n")

     

      #Write the resulted line to the file.

      outfile.write(res)

     

      #Close the file.

      outfile.close()

#Define the method amort_Sched().

def amort_Sched(self, amt_loan, month_int_rate, num_years):

   

    #Create another window.

    window = Tk()

   

    #Set the title of the window.

    window.title("Amortization Schedule")

   

    #Add text to the window.

    txt = Text(window) # Create and add text to the window

    txt.pack()

     

    #Declare the header line.

    line = "\n\nAmortization    Schedule\npmt#\t\tinterest\t\tprin pmt\t\tremianing prin\n"

   

    #Insert this line into the text.

    txt.insert(END, line)

   

    #Start the for loop.

    for i in range(1, num_years * 12 + 1):

     

      #Get the value of interest rate.

      int_rate = int(month_int_rate * amt_loan * 10) / 10.0

     

      #Get the principal amount.

      prin_amt = int((float(self.monthly_pay.get()) - int_rate) * 10) / 10.0

     

      #Get the amount of the loan.

      amt_loan = int((amt_loan - prin_amt) * 10) / 10.0

     

      #Get the resulted value.

      res = (str(i) + "\t\t$" + str(int_rate) + "\t\t$" + str(prin_amt) + "\t\t$" + str(amt_loan) + "\n")

     

      #Insert the resulted value to the text.

      txt.insert(END, res)

     

#Define the method get_mon_pay().

def get_mon_pay(self, loan, month_int_rate, num_years):

   

    #Calculate the montly payment.

    payOfMonth = loan * month_int_rate / (1 - 1 / (1 + month_int_rate) ** (num_years * 12))

   

    #Return the value of monthly payment.

    return payOfMonth;

#Call the LoanCalculator() class to create the required GUI.

LoanCalculator()

The UML diagram for the LoanCalculator class is shown as follows:

LoanCalculator

loan_amt : int ann_int_rate : float no_of_years : int mon_pay : float tot_pay : float mon_int_rate : float

calculate_pay() : void display_Shedule() : void printToFile(fname, loan, mon_int, num_years) : void amort_Sched(amt_loan, month_int_rate, num_years) : void get_mon_pay(loan, month_int_rate, num_years) : float

The name of the class is LoanCalculator. The class LoanCalculator has 6 attributes which are as follows:

·       loan_amt

·       ann_int_rate

·       no_of_years

·       mon_pay

·       tot_pay

·       mon_int_rate

The class LoanCalculator has 5 methods which are as follows:

·       calculate_pay(): This method is used to calculate the total payment and monthly payment.

·       display_Shedule(): This method is used to display the whole schedule of loan amount calculations.

·       printToFile(fname, loan, mon_int, num_years): This method is used to print the whole schedule of loan calculations on an output file.

·       amort_Sched(amt_loan, month_int_rate, num_years): This method is used for the amortization of the schedule of loan calculations and wrap the required lines in the text.

·       get_mon_pay(loan, month_int_rate, num_years): This method is used to calculate and return the monthly payment.