from tkinter import * # Use this if use python 3.xx
#from Tkinter import * # Use this if use python 2.xx
a = Button(text="Center Button")
b = Button(text="Top Left Button")
c = Button(text="Bottom Right Button")
a.place(relx=0.5, rely=0.5, anchor=CENTER)
b.place(relx=0.0, rely=0.0, anchor=NW)
c.place(relx=1.0, rely=1.0, anchor=SE)
mainloop()