from tkinter import *

class Calculator:
    
    def __init__(self, master):
        self.master = master
        master.title("Calculator")

        self.frame1 = Frame(master)
        self.frame1.option_add("*Font", "arial 20 bold")
        self.frame1.pack(expand=YES, fill=BOTH)

        self.num1 = 0
        self.num2 = 0
        self.final = 0
        self.method = 'none'
        
        self.result = StringVar()
        self.result.set("")

        self.entry = Entry(self.frame1, relief=FLAT, textvariable=self.result, justify='right', bd=5, bg='lightblue')
        self.entry.pack(side=TOP)

        self.frame2 = Frame(master, borderwidth=10, bd=1, bg="gray")
        self.frame2.pack(side=TOP, expand=YES, fill=BOTH)
        self.btnClear = Button(self.frame2, text = "C", width = 4, command = self.resetResult)
        self.btnClear.grid(column = 0, row = 0)
        self.btnCE = Button(self.frame2, text = "CE", width = 4, command = self.resetResult)
        self.btnCE.grid(column = 1, row = 0)

        #new new new
        self.btnPercent = Button(self.frame2, text = "%", width = 4, command = lambda: self.changeOp("%"))
        self.btnPercent.grid(column = 2, row = 0)
        

        for b in "123456789":
            btnNum = Button(self.frame2, text = b, width = 4, command = lambda n=b: self.numberUpdate(n))
            btnNum.grid(column = (int(b)-1)%3, row = int((int(b)-1)/3) + 1)

        self.btnDiv = Button(self.frame2, text = "/", width = 4, command = lambda: self.changeOp("/"))
        self.btnDiv.grid(column = 3, row = 0)

        self.btnTimes = Button(self.frame2, text = "*", width = 4, command = lambda: self.changeOp("*"))
        self.btnTimes.grid(column = 3, row = 1)

        self.btnSub = Button(self.frame2, text = "-", width = 4, command = lambda: self.changeOp("-"))
        self.btnSub.grid(column = 3, row = 2)

        self.btnAdd = Button(self.frame2, text = "+", width = 4, command = lambda: self.changeOp("+"))
        self.btnAdd.grid(column = 3, row = 3)

        ############# last row ##############
        
        self.btnDiv = Button(self.frame2, text = "+/-", width = 4, command = self.changeSign)
        self.btnDiv.grid(column = 0, row = 4)

        btnNum = Button(self.frame2, text = "0", width = 4, command = lambda n="0": self.numberUpdate(n))
        btnNum.grid(column = 1, row = 4)

        self.btnSub = Button(self.frame2, text = ".", width = 4, command = self.addDecimal)
        self.btnSub.grid(column = 2, row = 4)

        self.btnAdd = Button(self.frame2, text = "=", width = 4, command = self.getResult)
        self.btnAdd.grid(column = 3, row = 4)

    # homework starts below    
    def changeOp(self, op):
        pass
    
    def changeSign(self):
        pass

    def addDecimal(self):
        pass

    def getResult(self):
        pass
    
    def resetResult(self):
        self.num1 = 0
        self.num2 = 0
        self.final = 0
        self.method = 'none'
        self.result.set("")

    def numberUpdate(self, num):
        self.result.set(self.result.get()+num)
    
        

tk = Tk()
myCal = Calculator(tk)
tk.mainloop()