from tkinter import *



GRID_DICT = { 
    1: {"r": 2, "c": 0},
    2: {"r": 2, "c": 1},
    3: {"r": 2, "c": 2},
    4: {"r": 3, "c": 0},
    5: {"r": 3, "c": 1},
    6: {"r": 3, "c": 2},
    7: {"r": 4, "c": 0},
    8: {"r": 4, "c": 1},
    9: {"r": 4, "c": 2},
    0: {"r": 5, "c": 0},
    "+": {"r": 2, "c": 3},
    "-": {"r": 3, "c": 3},
    "*": {"r": 4, "c": 3},
    "/": {"r": 5, "c": 3},
    "=": {"r": 5, "c": 2},
    "c": {"r": 5, "c": 1},
    ".": {"r": 6, "c": 0},
}


expression = ""

def press(num):
    global expression
    expression = expression + str(num)
    equation .set(expression)

def equalpress():
    try:
        global expression
        total = str(eval(expression))
        equation.set(total)
        expression = ""        
    except:
        equation.set("error")
        expression = ""
        
def clear():
        global expression
        expression = ""
        equation.set("")
        
if __name__ == '__main__':
        gui = Tk()
        
        gui.configure(background="dark blue")
        gui.title("Simple calculator")
        gui.geometry("270x150")
        equation = StringVar()
        expression_field = Entry(gui, textvariable=equation)
        expression_field.grid(columnspan=6, ipadx=70)
        
        bn1 = Button(gui, text='1', fg='white', bg='blue', command=lambda: press(1), height=1, width=7)
        bn1.grid(row=GRID_DICT[1]["r"], column=GRID_DICT[1]["c"])  
        
        bn2 = Button(gui, text='2', fg='white', bg='blue', command=lambda: press(2), height=1, width=7)
        bn2.grid(row=GRID_DICT[2]["r"], column=GRID_DICT[2]["c"])
        
        bn3 = Button(gui, text='3', fg='white', bg='blue', command=lambda: press(3), height=1, width=7)
        bn3.grid(row=GRID_DICT[3]["r"], column=GRID_DICT[3]["c"])
        
        bn4 = Button(gui, text='4', fg='white', bg='blue', command=lambda: press(4), height=1, width=7)
        bn4.grid(row=GRID_DICT[4]["r"], column=GRID_DICT[4]["c"])
        
        bn5 = Button(gui, text='5', fg='white', bg='blue', command=lambda: press(5), height=1, width=7)
        bn5.grid(row=GRID_DICT[5]["r"], column=GRID_DICT[5]["c"])
        
        bn6 = Button(gui, text='6', fg='white', bg='blue', command=lambda: press(6), height=1, width=7)
        bn6.grid(row=GRID_DICT[6]["r"], column=GRID_DICT[6]["c"])
        
        bn7 = Button(gui, text='7', fg='white', bg='blue', command=lambda: press(7), height=1, width=7)
        bn7.grid(row=GRID_DICT[7]["r"], column=GRID_DICT[7]["c"])
        
        bn8 = Button(gui, text='8', fg='white', bg='blue', command=lambda: press(8), height=1, width=7)
        bn8.grid(row=GRID_DICT[8]["r"], column=GRID_DICT[8]["c"])
        
        bn9 = Button(gui, text='9', fg='white', bg='blue', command=lambda: press(9), height=1, width=7)
        bn9.grid(row=GRID_DICT[9]["r"], column=GRID_DICT[9]["c"])
        
        bn0 = Button(gui, text='0', fg='white', bg='blue', command=lambda: press(0), height=1, width=7)
        bn0.grid(row=GRID_DICT[0]["r"], column=GRID_DICT[0]["c"])
        
        plus = Button(gui, text='+', fg='white', bg='blue', command=lambda: press("+"), height=1, width=7)
        plus.grid(row=GRID_DICT["+"]["r"], column=GRID_DICT["+"]["c"])

        minus = Button(gui, text='-', fg='white', bg='blue', command=lambda: press("-"), height=1, width=7)
        minus.grid(row=GRID_DICT["-"]["r"], column=GRID_DICT["-"]["c"])        
        
        multiply = Button(gui, text='*', fg='white', bg='blue', command=lambda: press("*"), height=1, width=7)
        multiply.grid(row=GRID_DICT["*"]["r"], column=GRID_DICT["*"]["c"])

        divide = Button(gui, text='/', fg='white', bg='blue', command=lambda: press("/"), height=1, width=7)
        divide.grid(row=GRID_DICT["/"]["r"], column=GRID_DICT["/"]["c"]) 
        
        equals = Button(gui, text='=', fg='white', bg='blue', command=equalpress, height=1, width=7)
        equals.grid(row=GRID_DICT["="]["r"], column=GRID_DICT["="]["c"])
        
        clear = Button(gui, text='C', fg='white', bg='blue', command=clear, height=1, width=7)
        clear.grid(row=GRID_DICT["c"]["r"], column=GRID_DICT["c"]["c"])
        
        dec = Button(gui, text='.', fg='white', bg='blue', command=lambda: press("."), height=1, width=7)
        dec.grid(row=GRID_DICT["."]["r"], column=GRID_DICT["."]["c"])
        
        gui.mainloop()