from tkinter import *

a=""

def press(n):
    global a
    a+=str(n)
    equation.set(a)
    
def equalpress():
    try:
        global a
        t=str(eval(a))
        equation.set(t)
        a=""
    except:
        equation.set("Error")
        a=""
        
def clear():
    global a
    a=""
    equation.set("")
   
if __name__=="__main__":
    gui=Tk()
    gui.configure(background="black")
    gui.title("Calculator")
    gui.geometry("260x150")
    equation=StringVar()
    a_field=Entry(gui,textvariable=equation)
    a_field.grid(columnspan=4,ipadx=70)
    equation.set
    
button1=Button(gui,text="1",fg="black",bg="white",command=lambda:press(1),height=1,width=7)
button1.grid(row=2,column=0)

button2=Button(gui,text="2",fg="black",bg="white",command=lambda:press(2),height=1,width=7)
button2.grid(row=2,column=1)

button3=Button(gui,text="3",fg="black",bg="white",command=lambda:press(3),height=1,width=7)
button3.grid(row=2,column=2)

button4=Button(gui,text="4",fg="black",bg="white",command=lambda:press(4),height=1,width=7)
button4.grid(row=3,column=0)

button5=Button(gui,text="5",fg="black",bg="white",command=lambda:press(5),height=1,width=7)
button5.grid(row=3,column=1)

button6=Button(gui,text="6",fg="black",bg="white",command=lambda:press(6),height=1,width=7)
button6.grid(row=3,column=2)

button7=Button(gui,text="7",fg="black",bg="white",command=lambda:press(7),height=1,width=7)
button7.grid(row=4,column=0)

button8=Button(gui,text="8",fg="black",bg="white",command=lambda:press(8),height=1,width=7)
button8.grid(row=4,column=1)

button9=Button(gui,text="9",fg="black",bg="white",command=lambda:press(9),height=1,width=7)
button9.grid(row=4,column=2)

button0=Button(gui,text="0",fg="black",bg="white",command=lambda:press(0),height=1,width=7)
button0.grid(row=5,column=0)

plus=Button(gui,text="+",fg="black",bg="white",command=lambda:press("+"),height=1,width=7)
plus.grid(row=2,column=3)

minus=Button(gui,text="-",fg="black",bg="white",command=lambda:press("-"),height=1,width=7)
minus.grid(row=3,column=3)

multiply=Button(gui,text="*",fg="black",bg="white",command=lambda:press("*"),height=1,width=7)
multiply.grid(row=4,column=3)

divide=Button(gui,text="/",fg="black",bg="white",command=lambda:press("/"),height=1,width=7)
divide.grid(row=5,column=3)

equal=Button(gui,text="=",fg="black",bg="white",command=equalpress,height=1,width=7)
equal.grid(row=5,column=2)

clear=Button(gui,text="C",fg="black",bg="white",command=clear,height=1,width=7)
clear.grid(row=5,column=1)

decimal=Button(gui,text=".",fg="black",bg="white",command=lambda:press("."),height=1,width=7)
decimal.grid(row=6,column=0)

gui.mainloop()