Simple Calculator using Tkinter:
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def addition(a,b):
	return a+b

addition(12,13)

from tkinter import *

import math

class Calculator:
    def getandreplace(self):
        self.expression = self.e.get()
        self.newtext = self.expression.replace('/','/')
        self.newtext = self.newtext.replace('x','*')

    def equals(self):
        self.getandreplace()
        try:
            self.value = eval(self.newtext)
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input!')
        else:
            self.e.delete(0,END)
            self.e.insert(0,self.value)

    def squareroot(self):
        self.getandreplace()
        try:
            self.value = eval(self.newtext)
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input!')
        else:
            self.sqrtval = math.sqrt(self.value)
            self.e.delete(0,END)
            self.e.insert(0,self.sqrtval)

    def square(self):
        self.getandreplace()
        try:
            self.value = eval(self.newtext)
        except SyntaxError or NameError:
            self.e.delete(0,END)
            self.e.insert(0,'Invalid Input')
        else:
            self.sqval = math.pow(self.value,2)
            self.e.delete(0,END)
            self.e.insert(0,self.sqval)

    def clearall(self):
        self.e.delete(0,END)

    def clear1(self):
        self.txt = self.e.get()[::-1]
        self.e.delete(0,END)
        self.e.insert(0,self.txt)

    def action(self,argi):
        self.e.insert(END,argi)

    def __init__(self,master):
        master.title('Calculator')
        master.geometry()
        self.e = Entry(master)
        self.e.grid(row = 0,column = 0, columnspan = 6, pady = 3)
        self.e.focus_set()

        Button(master,text = "=",width = 11, height = 3,fg = "blue",bg = "orange",command = lambda:self.equals()).grid(row = 4,column = 4,columnspan = 2)

        Button(master,text = "AC", width = 5, height = 3, fg = "red",bg = "light green", command = lambda:slef.clearall()).grid(row = 1, column = 4)

        Button(master,text = "C", width = 5,height = 3, fg = "red", bg = "light green",command = lambda:self.clear1()).grid(row = 1, column = 5)

        Button(master,text = "+",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('+')).grid(row = 4, column = 3)

        Button(master,text = "X",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('X')).grid(row = 2, column = 3)

        Button(master,text = "-",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('-')).grid(row = 3, column = 3)

        Button(master,text = "÷",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('/')).grid(row = 1, column = 3)

        Button(master,text = "%",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('%')).grid(row = 4, column = 2)

        Button(master,text = "7",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('7')).grid(row = 1, column = 0)

        Button(master,text = "8",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('8')).grid(row = 1, column = 1)

        Button(master,text = "9",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('9')).grid(row = 1, column = 2)

        Button(master,text = "4",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('4')).grid(row = 2, column = 0)

        Button(master,text = "5",width = 5,height = 3,fg = "blue",bg = "orange",command = lambda:self.action('5')).grid(row = 2, column = 1)

        Button(master,text = "6",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('6')).grid(row = 2, column = 2)

        Button(master,text = "1",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('1')).grid(row = 3, column = 0)

        Button(master,text = "2",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('2')).grid(row = 3, column = 1)

        Button(master,text = "3",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('3')).grid(row = 3, column = 2)

        Button(master,text = "0",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('0')).grid(row = 4, column = 0)

        Button(master,text = ".",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('.')).grid(row = 4, column = 1)

        Button(master,text = "(",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('(')).grid(row = 2, column = 4)

        Button(master,text = ")",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action(')')).grid(row = 2, column = 5)

        Button(master,text = "?",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action('?')).grid(row = 3, column = 4)

        Button(master,text = ":",width = 5,height = 3,fg = "red",bg = "light green",command = lambda:self.action(':')).grid(row = 3, column = 5)


window = Tk()

obj = Calculator(window)

window.mainloop()