Mini Jogo

from tkinter import *
root =Tk()
class app():
    def __init__(self):
        self.root = root
        self.janela()
        self.minojogo()
        root.mainloop()
    def janela(self):
        self.root.title("Mini Jogo")
        self.root.geometry("300x250")
        self.root.configure(background='Gray')
        self.root.resizable(False, False)
    def minojogo(self):
        self.v = StringVar()
        self.pergunta_lb = Label(textvariable= self.v,
                                   font=("Helvetica", '20'))
        self.pergunta_lb.place(relx=0.2, rely=0.15)
        self.v.set("Quanto é 1 + 1 ?")
        self.um = Button( text="1", font=("Helvetica", 20), command=self.um)
        self.um.place(relx=0.25,rely=0.4)
        self.dois = Button( text="2", font=("Helvetica", 20), command=self.dois)
        self.dois.place(relx=0.45, rely=0.4)
        self.tres = Button( text="3", font=("Helvetica", 20), command=self.tres)
        self.tres.place(relx=0.65, rely=0.4)
    def um(self):
        self.v.set('Você errou!!')
    def dois(self):
        self.v.set('Você acertou!!')
    def tres(self):
        self.v.set('Você errou!!')
app()