message entry box at center

[asit]

from Tkinter import *


def callback():
print e.get()


master=Tk()
e=Entry(master)
e.pack(anchor=CENTER)
e.focus_set()


b=Button(master,text="get",width=10,command=callback)
b.pack(anchor=CENTER)

master.mainloop()


i want to show the entry button at the center of the window. How is it
possible ??