from tkinter import *

janela = Tk()


lb1 = Label(janela, text='horizontal', bg='white')
lb1.pack(side=TOP, fill=X)

lb2 = Label(janela, text='', bg='black')
lb2.pack(side=LEFT, fill=Y)

lb3 = Label(janela, text='', bg='black')
lb3.pack(side=RIGHT, fill=Y)



janela.geometry('500x200+-600+200')
janela.mainloop()