Equação do 2º Grau usandoTkinter

from tkinter import *
import math
root = Tk()
class equacaosegundograu():
    def __init__(self):
        self.root = root
        self.janela()
        self.dados()
        # criando o Loop
        root.mainloop()
    def janela(self):
        self.root.title("Equação de Segundo Grau)")
        self.root.configure(background= '#B0C4DE')
        self.root.geometry("350x150")
        self.root.resizable(False, False)
    def dados(self):
        self.a_entrada = IntVar()
        self.lb_a = Label(text='A:',
                                       font=('Verdana', '8', 'bold'),
                                       bg='#D3D3D3', fg='#000000')
        self.lb_a.place(relx=0.3, rely=0.05, relwidth=0.1,
                                     relheight=0.1)
        self.input_a = Entry(textvariable=self.a_entrada)
        self.input_a.place(relx=0.45, rely=0.05, relwidth=0.15,
                                        relheight=0.1)

        self.b_entrada = IntVar()
        self.lb_b = Label(text='B:',
                          font=('Verdana', '8', 'bold'),
                          bg='#D3D3D3', fg='#000000')
        self.lb_b.place(relx=0.3, rely=0.2, relwidth=0.1,
                        relheight=0.1)
        self.input_b = Entry(textvariable=self.b_entrada)
        self.input_b.place(relx=0.45, rely=0.2, relwidth=0.15,
                           relheight=0.1)

        self.c_entrada = IntVar()
        self.lb_c = Label(text='C:',
                          font=('Verdana', '8', 'bold'),
                          bg='#D3D3D3', fg='#000000')
        self.lb_c.place(relx=0.3, rely=0.35, relwidth=0.1,
                        relheight=0.1)
        self.input_c = Entry(textvariable=self.c_entrada)
        self.input_c.place(relx=0.45, rely=0.35, relwidth=0.15,
                           relheight=0.1)
#
        self.bt_calcular = Button( text='Calcular',
                                 font=("verdana", 10, "bold"),
                                   command = self.butaoclick1)
        self.bt_calcular.place(relx=0.3, rely=0.5, relwidth=0.4,relheight = 0.17)
        #Resultado
        self.resulfinal = StringVar()
        self.resulfinal_ld = Label(textvariable=self.resulfinal)
        self.resulfinal_ld.place(relx=0.1, rely=0.7, relwidth=0.8,relheight=0.2)

    def butaoclick1(self):
        a = self.a_entrada.get()
        b = self.b_entrada.get()
        c = self.c_entrada.get()
        delta = pow(b, 2) - (4 * a * c)
        if delta == 0:
            x = -b / (2 * a)
            xr = round(x,2)
            final = 'O X de ' + str(x)
        elif delta <0:
            final='Delta menor que 0. Raízes imaginárias.'
        else:
            x1 = (-b + math.sqrt(delta)) / (2 * a)
            x1r = round(x1, 2)
            x2 = (-b - math.sqrt(delta)) / (2 * a)
            x2r = round(x2, 2)
            final = 'O x1 igual ' + str(x1r) + " ou x2 igual " + str(x2r)
        return self.resulfinal.set(final)
equacaosegundograu()