[Tkinter] Getting Input from Tkinter Entry

[juliabrushett]

Hello,

I am wanting to do some calculations using interest, total amount, and years to pay of an item, but I am having trouble getting and using the user input from a tkinter entry. Can someone help guide me through this process? My code so far is below:

import math
from tkinter import *

def calculatePayment(amount, intRate, years) :
    amount = entAmount.get()
    intRate = entIntRate.get()
    years = entYears.get()
    interest = intRate / 100
    interest = interest / 12
    payment = (amount * interest) / (1 - (math.pow(1 / (1 + interest), years * 12)))
    #lblMonthlyPayment = Label(main, text = payment)
    #lblTotalPayment = Label(main, text = payment * 12 * years)
    return payment

main = Tk()
main.title("How Much?")
main.geometry('300x300')

lblAmount = Label(main, text = 'Amount of Purchase:')
lblAmount.grid(row = 0, column = 0, padx = 0, pady = 10)
a = StringVar()
entAmount = Entry(main, width = 20)
entAmount.grid(row = 0, column = 1)

lblIntRate = Label(main, text = 'Interest Rate (like 7.5):')
lblIntRate.grid(row = 1, column = 0, padx = 0, pady = 10)
entIntRate = Entry(main, width = 20)
entIntRate.grid(row = 1, column = 1)

lblYears = Label(main, text = 'Years to Pay:')
lblYears.grid(row = 2, column = 0, padx = 0, pady = 10)
entYears = Entry(main, width = 20)
entYears.grid(row = 2, column = 1)

lblMonthly = Label(main, text = 'Monthly Payment:')
lblMonthly.grid(row = 3, column = 0, padx = 0, pady = 10)
lblMonthly.bind(calculatePayment)

lblTotal = Label(main, text = 'Total Purchase Cost:')
lblTotal.grid(row = 4, column = 0, padx = 0, pady = 10)

btn = Button(BOTTOM, text = 'Calculate', command = calculatePayment)
btn.pack()

main.mainloop()

---

Ignore the StringVar "a" on line 21, that was something else I was trying that I forgot to remove from the code before posting

---

Okay, adjusted again. Now I am just having trouble calling my function, I think. Here is my error message when trying to run code:
Traceback (most recent call last):
File "C:\Users\Julia\Desktop\Python\Assignment16\Assignment16\Assignment16.py", line 39, in <module>
monthpayment = calculatePayment()
File "C:\Users\Julia\Desktop\Python\Assignment16\Assignment16\Assignment16.py", line 11, in calculatePayment
amt = float(amount.get())
ValueError: could not convert string to float:
Press any key to continue . . .

Here is my adjusted code:

import math
from tkinter import *

def calculatePayment() :
    amt = float(amount.get())
    itrt = float(intRate.get())
    yrs = float(years.get())
    interest = itrt / 100
    interest = interest / 12
    payment = (amt * interest) / (1 - (math.pow(1 / (1 + interest), yrs * 12)))
    return payment

main = Tk()
main.title("How Much?")
main.geometry('300x300')

amount = StringVar()
intRate = StringVar()
years = StringVar()

lblAmount = Label(main, text = 'Amount of Purchase:').grid(row = 0, column = 0, padx = 0, pady = 10)
entAmount = Entry(main, textvariable = amount).grid(row = 0, column = 1)

lblIntRate = Label(main, text = 'Interest Rate (like 7.5):').grid(row = 1, column = 0, padx = 0, pady = 10)
entIntRate = Entry(main, textvariable = intRate).grid(row = 1, column = 1)

lblYears = Label(main, text = 'Years to Pay:').grid(row = 2, column = 0, padx = 0, pady = 10)
entYears = Entry(main, textvariable = years).grid(row = 2, column = 1)


btn = Button(main, text = 'Calculate', command = calculatePayment).grid(row = 5, column = 1)

monthpayment = calculatePayment()
lblMonthly = Label(main, text = 'Monthly Payment: $ %.2f' % monthpayment).grid(row = 3, column = 0, padx = 0, pady = 10)
totpayment = monthpayment * 12 * float(years)
lblTotal = Label(main, text = 'Total Purchase Cost:' % totpayment).grid(row = 4, column = 0, padx = 0, pady = 10)

main.mainloop()

---

Okay, I figured it out! For anyone who may want to see, here is my final code:

import math
from tkinter import *

def calculatePayment() :
    amt = float(amount.get())
    itrt = float(intRate.get())
    yrs = float(years.get())
    interest = itrt / 100
    interest = interest / 12
    payment = (amt * interest) / (1 - (math.pow(1 / (1 + interest), yrs * 12)))
    lblMonthly = Label(main, text = '$ %.2f' % payment).grid(row = 3, column = 1, padx = 0, pady = 10)
    totpayment = payment * 12 * yrs
    lblTotal = Label(main, text = '$ %.2f' % totpayment).grid(row = 4, column = 1, padx = 0, pady = 10)
    return

main = Tk()
main.title("How Much?")
main.geometry('300x300')

amount = StringVar()
intRate = StringVar()
years = StringVar()

lblAmount = Label(main, text = 'Amount of Purchase:').grid(row = 0, column = 0, padx = 0, pady = 10)
entAmount = Entry(main, textvariable = amount).grid(row = 0, column = 1)

lblIntRate = Label(main, text = 'Interest Rate (like 7.5):').grid(row = 1, column = 0, padx = 0, pady = 10)
entIntRate = Entry(main, textvariable = intRate).grid(row = 1, column = 1)

lblYears = Label(main, text = 'Years to Pay:').grid(row = 2, column = 0, padx = 0, pady = 10)
entYears = Entry(main, textvariable = years).grid(row = 2, column = 1)


btn = Button(main, text = 'Calculate', command = calculatePayment).grid(row = 5, column = 1)

lblMonthly = Label(main, text = 'Monthly Payment:').grid(row = 3, column = 0, padx = 0, pady = 10)
lblTotal = Label(main, text = 'Total Purchase Cost:').grid(row = 4, column = 0, padx = 0, pady = 10)

main.mainloop()