Pig Latin (usando Tkinter)

from tkinter import *

root = Tk()
root.geometry("400x400")
root.resizable(0, 0)
root.config(bg="#103030")
root.title("Pig Latin")

titulo = Label(text="Pig Latin",
               font=("Arial", "55", "bold"), bg="#103030", fg="#49e3e3")
titulo.place(relx=0.1, rely=0.05)

texto_sub1 = Label(text="Frase:",
                   font=("Arial", "20", "bold"), bg="#103030", fg="#49e3e3")
texto_sub1.place(relx=0.1, rely=0.35)

frase = StringVar()
frase_entrada = Entry(textvariable=frase,
                      font=("Arial", "12", "bold"),
                      bg="white", fg="blue", justify='center')
frase_entrada.place(relx=0.33, rely=0.37, relwidth=0.63)

def limpar():
    frase_entrada.delete(0, END)
    resultado.set("")

def app():
    f = frase.get().lower().split()
    frase_final = []
    for palavra in f:
        if palavra[0] in "aeiou":
            palavra = palavra + "yay"
        else:
            palavra = palavra[1:] + palavra[0] + "ay"
        frase_final.append(palavra)
    resultado.set(" ".join(frase_final))

but1 = Button(text="Mostrar", bd=2, bg='#107db2', fg='white',
              font=('verdana', 12, 'bold'), command=app)
but1.place(relx=0.1, rely=0.55, 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=0.4, rely=0.55, 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=0.7, rely=0.55, relwidth=0.25, relheight=0.1)

resultado = StringVar()
resultado_texto = Label(textvariable=resultado,
                        font=("Arial", 12, "bold"), bg="#cfe2f3")
resultado_texto.place(relx=0.05, rely=0.68, relwidth=0.9, relheight=0.3)

root.mainloop()