Simple Calculator using Tkinter

import tkinter as tk

root = tk.Tk()

root.title('BASIC CALCULATOR')

root.geometry('640x480+300+300')

root.resizable(False, False)

title = tk.Label(

 root,

 text='Simple Calculator',

 font=('Timesnewroman 18 bold'),

 bg='green',

 fg='#AB1'

)

var1=tk.DoubleVar()

var2=tk.DoubleVar()

var1_label = tk.Label(root, text='Number1: ')

var1_inp = tk.Entry(root, textvariable=var1)

var2_label = tk.Label(root, text='Number: ')

var2_inp = tk.Entry(root, textvariable=var2)

plus_btn = tk.Button(root, text=' + ')

minus_btn = tk.Button(root, text=' - ')

mul_btn=tk.Button(root,text='*')

divide_btn=tk.Button(root,text='/')

output_var = tk.StringVar(value='')

output_line = tk.Label(

 root,

 textvariable=output_var,

 anchor='w',

 justify='left'

)

title.grid(columnspan=4)

var1_label.grid(row=10,column=0)

var1_inp.grid(row=10,column=1)

var2_label.grid(row=10,column=2)

var2_inp.grid(row=10,column=3)

plus_btn.grid(row=99,column=0)

minus_btn.grid(row=99,column=1)

mul_btn.grid(row=99,column=2)

divide_btn.grid(row=99,column=3)

output_line.grid(row=100, columnspan=2, sticky='NSEW')

root.columnconfigure(1, weight=1)

root.rowconfigure(99, weight=2)

root.rowconfigure(100, weight=1)

def on_plus_submit():

 """To be run when the user submits the form"""

 val1 = var1.get()

 val2=var2.get()

 mysum=val1+val2

 message = f'sum is , {mysum}.\n'

 output_var.set(message)

def on_minus_submit():

 """To be run when the user submits the form"""

 val1 = var1.get()

 val2=var2.get()

 minus=val1-val2

 message = f'difference is , {minus}.\n'

 output_var.set(message)

def on_mul_submit():

 """To be run when the user submits the form"""

 val1 = var1.get()

 val2=var2.get()

 mul=val1*val2

 message = f'multiplication is , {mul}.\n'

 output_var.set(message)

def on_divide_submit():

 """To be run when the user submits the form"""

 val1 = var1.get()

 val2=var2.get()

 divide=val1/val2

 message = f'division is , {divide}.\n'

 output_var.set(message)

plus_btn.configure(command=on_plus_submit)

minus_btn.configure(command=on_minus_submit)

mul_btn.configure(command=on_mul_submit)

divide_btn.configure(command=on_divide_submit)

root.mainloop()