[Tutor] Newbie struggling with Tkinter/canvas tags

[Glen]

As a Python/Tkinter newbie, I thought I was getting on ok... 
then I hit this problem.

I have a canvas (c1)
A group of objects are drawn on c1 and given a tag
	c1.addtag_all('group_A')
	
Another group of objects are drawn, I wish to tag these 'group_B'.
At the moment I 'get by' with...

    a=c1.find_withtag('group_A')
    b=c1.find_all()
    c=b[len(a):]
    for i in range(len(c)):
        c1.addtag_above('group_B',len(a)+i)

I'm sure there's a "nicer" method than this, but I can't see it.
Any help would be greatly appreciated.
Thanks