simple_gui_calculator.py

from tkinter import *

root = Tk()
root.title("Calculator")

e = Entry(root, width=35, borderwidth=5)
e.grid(row=0, column=0, columnspan=3, padx=10, pady=10)

def button_click(number):
	current = e.get()
	e.delete(0, END)
	e.insert(0, str(current) + str(number))

def button_clear():
	e.delete(0, END)

def button_add():
	first = e.get()
	global f_num
	global math
	math = "addition"
	f_num = int(first)
	e.delete(0, END)

def button_sub():
	first = e.get()
	global f_num
	global math
	math = "subtraction"
	f_num = int(first)
	e.delete(0, END)	

def button_mul():
	first = e.get()
	global f_num
	global math
	math = "multiplication"
	f_num = int(first)
	e.delete(0, END)

def button_div():
	first = e.get()
	global f_num
	global math
	math = "division"
	f_num = int(first)	
	e.delete(0, END)

def button_equal():
	second = e.get()
	s_num = int(second)
	e.delete(0, END)
	if math == "addition":
		e.insert(0, f_num + s_num)
	elif math == "subtraction":
		e.insert(0, f_num - s_num)
	elif math == "multiplication":
		e.insert(0, f_num * s_num)
	elif math == "division":
		e.insert(0, f_num / s_num)


#Buttons definition
button_1 = Button(root, text="1", padx=40, pady=20, command=lambda: button_click(1))
button_2 = Button(root, text="2", padx=40, pady=20, command=lambda: button_click(2))
button_3 = Button(root, text="3", padx=40, pady=20, command=lambda: button_click(3))
button_4 = Button(root, text="4", padx=40, pady=20, command=lambda: button_click(4))
button_5 = Button(root, text="5", padx=40, pady=20, command=lambda: button_click(5))
button_6 = Button(root, text="6", padx=40, pady=20, command=lambda: button_click(6))
button_7 = Button(root, text="7", padx=40, pady=20, command=lambda: button_click(7))
button_8 = Button(root, text="8", padx=40, pady=20, command=lambda: button_click(8))
button_9 = Button(root, text="9", padx=40, pady=20, command=lambda: button_click(9))
button_0 = Button(root, text="0", padx=91, pady=20, command=lambda: button_click(0))

button_add = Button(root, text="+", padx=40, pady=20, command=button_add)
button_sub = Button(root, text="-", padx=40, pady=20, command=button_sub)
button_mul = Button(root, text="*", padx=40, pady=20, command=button_mul)
button_div = Button(root, text="/", padx=40, pady=20, command=button_div)
button_equal = Button(root, text="=", padx=40, pady=20, command=button_equal)
button_clear = Button(root, text="clear", padx=80, pady=20, command=button_clear)


#Button Grids
button_1.grid(row=1, column=0)
button_2.grid(row=1, column=1)
button_3.grid(row=1, column=2)
button_4.grid(row=2, column=0)
button_5.grid(row=2, column=1)
button_6.grid(row=2, column=2)
button_7.grid(row=3, column=0)
button_8.grid(row=3, column=1)
button_9.grid(row=3, column=2)
button_0.grid(row=4, column=0, columnspan=2)

button_add.grid(row=1, column=3)
button_sub.grid(row=2, column=3)
button_mul.grid(row=3, column=3)
button_div.grid(row=4, column=3)
button_equal.grid(row=4, column=2)
button_clear.grid(row=5, column=2, columnspan=2)

root.mainloop()