Question on Pmw Balloon Binding

[Geiger Ho]

Hi all,

  I want to create a balloon help for a button. So I have the following
code:

from Tkinter import *
import Pmw
root = Tk()
Pmw.initialise(root)
frame = Frame(root).pack()
button = Button(frame, text="Button").pack()
balloon = Pmw.Balloon(root)
balloon.bind(button, "Button")

However, when I run the code I get the following error:

File "myprog.py", line 8, in ?
  balloon.bind(button, "Button")
File "..../PmwBalloon.py", line 67, in bind
  enterID = widget.bind('<Enter>',
AttributeError: 'NoneType' object has no atribute 'bind'

When I modify the code as:

button = Button(frame, text="Button")
button.pack()
balloon = Pmw.Balloon(root)
balloon.bind(button, "Button")

It works!
Why? Can anyone tell me the reasons behind.

Thanks in advance.

Regards,
Geiger