Tkinter tutorial?

[Walter Hurry]

I have some experience with Python, having used it for a couple of years.

Until now, my builder of choice for cross-platform GUI applications has 
been wxPython (with wxGlade), and I have been well satisfied with these 
tools.

However, for a different project I need to get up to a reasonable speed 
with tkinter. Could some kind soul recommend a suitable on-line tutorial, 
or a (free) ebook?

Thanks.