Hmm. This might be associated with another problem I've been having. NOT really tried--not near a python interpreter... If I have something like: x = [1,2,3,4,5,6] y = x then changes to y change x. So I've had to: y = [x[0],x[1],x[2],x[3],x[4],x[5]] ...which doesn't change x when y is changed.