from tkinter import *
import tkinter
import tkMessageBox



top = tkinter.Tk()

def helloCallBack():
   tkMessageBox.showinfo( "Hello Python", "Hello World")

B = Tkinter.Button(top, text ="Hello", command = helloCallBack)

B.pack()
B.place(bordermode=OUTSIDE, height=100, width=100)
top.mainloop()