Converting a list of lists to a single list

[steve at divillo.com]

I think that itertools may be able to do what I want but I have not been able to figure out how.

I want to convert an arbitrary number of lists with an arbitrary number of elements in each list into a single list as follows.

Say I have three lists:

[[A0,A1,A2], [B0,B1,B2] [C0,C1,C2]]

I would like to convert those to a single list that looks like this:

[A0,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2,A1,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2,A2,B0,C0,C1,C2,B1,C0,C1,C2,B2,C0,C1,C2]

An easier way to visualize the pattern I want is as a tree.

A0
	B0
		C0
		C1
		C2
	B1
		C0
		C1
		C2
	B2
		C0
		C1
		C2
A1
	B0
		C0
		C1
		C2
	B1
		C0
		C1
		C2
	B2
		C0
		C1
		C2
A2
	B0
		C0
		C1
		C2
	B1
		C0
		C1
		C2
	B2
		C0
		C1
		C2