Detector de Palíndromo (usando Tkinter)

from tkinter import *
root = Tk()
root.geometry("400x400")
root.resizable(0, 0)
root.config(bg="#d9ead3")
root.title("Detector de Palíndromo")
def limpar():
    frase_entrada.delete(0, END)
def app():
    f = frase.get()
    fp = f.strip().split()
    junto = ''.join(fp).upper()
    inverso = junto[::-1]
    if inverso == junto:
          teste = 'A frase digitada é um palindromo'
    else:
         teste ='A frase não e um palindromo'

    mensagem = f'A frase {junto}\nIvertida e {inverso}\n{teste}'
    resultado.set(mensagem)

titulo = Label(text="Detector de Palíndromo",
               font=("Arial", "15", "bold"),bg="#d9ead3",fg="#bf9000")
titulo.place(relx=0.25, rely=0.05)
texto_sub1  = Label(text="Frase:",
                    font=("Arial", "12", "bold"),bg="#d9ead3",fg="#bf9000")
texto_sub1.place(relx=0.15, rely=0.2)

frase = StringVar()
frase_entrada = Entry(textvariable=frase,
                             font=("Arial", "12", "bold"),
                             bg="white", fg="blue", justify='center')
frase_entrada.place(relx=0.3, rely=0.2, relwidth=0.65)

but1 = Button(text="Verificar", bd=2, bg='#107db2', fg='white',
              font=('verdana', 12, 'bold'), command=app)
but1.place(relx=0.05, rely=0.3, relwidth=0.25, relheight=0.1)
but_limpar = Button(text="Limpar", bd=2, bg='#107db2', fg='white',
                    font=('verdana', 12, 'bold'), command=limpar)
but_limpar.place(relx=0.35, rely=0.3, relwidth=0.25, relheight=0.1)

but_sair = Button(text="Sair", bd=2, bg='#107db2', fg='white',
                    font=('verdana', 12, 'bold'), command=root.destroy)
but_sair.place(relx=0.65, rely=0.3, relwidth=0.25, relheight=0.1)

resultado = StringVar()
resultado_texto = Label(textvariable=resultado,
                           font=("Arial", 12, "bold"), bg="#cfe2f3")
resultado_texto.place(relx=0.2, rely=0.5, relwidth=0.7,relheight=0.4)
root.mainloop()