I'm not sure if this is the intended behavior, but it seems unusual to me.
a = [set([]) for i in range(2)] evaluates to a list [set([]),set([])] and
b= 2*[set([])] evaluates to [set([]),set([])].
Nothing wrong here. 
Nevertheless, if I do a[0].add(1), a has the value [set([1]), set([])] but  b[0].add(1) evaluates to [set([1]), set([1])]. 
I understand that in list b, all of the sets refer to the same object in memory, nevertheless, I do not feel like this is the correct behavior.