> a=((2,4),(4,2)) THese are tuples. You aren't allowed to change tuples, they are whats called immutable. You can create lists from them and change those, or just start with lists in the first place: a = [[2,4],[4,2]] a[1][1] = 4 Should now work. HTH Alan G Author of the Learn to Program web tutor http://www.freenetpages.co.uk/hp/alan.gauld