Я не могу пройти мимо этой ошибки в Tkinter

Question

Я пытаюсь сделать игру, используя Tkinter, считая до 21 (2 игрока по очереди выбирают число от 1 до 3, при этом человек вынужден выбрать 21 проигрыш). На данный момент мой код создает интерфейс, но я не уверен, как заставить кнопки добавлять 1,2 или 3 к общему числу при нажатии.

(вот код ниже, любая помощь будет с благодарностью)

from random import randrange
window = tk.Tk()



window.title("Guessing Game")

lblInst = tk.Label(window, text = "Pick a number between 1-3")
lblLine0 = tk.Label(window, text = "*********************************************************************")

lblLine1 = tk.Label(window, text = "*********************************************************************")
lblLogs = tk.Label(window, text="Game Logs")


totnumber = ''

#buttons

def press(playernu): 
    global totnumber 

    totnumber = totnumber + str(playernu)
    totnumber.set(totnumber) 


# create the buttons


button1 = tk.Button(window, text=' 1 ', fg='black', bg='red', 
                     command=lambda: press(1), height=1, width=7)
button2 = tk.Button(window, text=' 2 ', fg='black', bg='red', 
                     command=lambda: press(2), height=1, width=7) 
button3 = tk.Button(window, text=' 3 ', fg='black', bg='red', 
                     command=lambda: press(3), height=1, width=7)



# append elements to grid
lblInst.grid(row=0, column=0, columnspan=5)
lblLine0.grid(row=1, column=0, columnspan=5)


button1.grid(row=2, column=0, columnspan=3)
button2.grid(row=2, column=1, columnspan=3)
button3.grid(row=2, column=2, columnspan=3)


lblLine1.grid(row=3, column=0, columnspan=5)
lblLogs.grid(row=4, column=0, columnspan=5)  


# Main game logic


def process():
    global totnumber, playernu, button1, button2, button3

    while totnumber < 21:
        lbl = tk.Label(window, text="It is your turn ", fg="black")


        totnumber = totnumber + playernum
        lbl = tk.Label(window, text="It is your turn "+ str(totnumber), fg ="black")

        if totnumber > 20:
                lbl = tk.Label(window, text="You Lose "+ str(totnumber), fg="red")
                break

        else:
                pass

            #computer turn

        PCnum = random.randrange(1, 3)           
        lbl = tk.Label(window, text="It is now my turn ", fg="black")
        lbl = tk.Label(window, text="I pick "+ str(PCnum), fg="black")

        totnumber = PCnum + totnumber
        lbl = tk.Label(window, text="the total number is now " + str(totnumber), fg="black")

        if totnumber > 20:
            lbl = tk.Label(window, text="welp I guess I lose this one traveller ", fg="green")
            break
        else:
            pass```