comparing [x for x in list1 if x not in list2] with set1, set2 = set(list1), set(list2) list(set1-set2)
gives something like len(list2) speedup ------------------------------ 100 10 1000 100 10000 1000 the speedup is constant for different len(list1) -- http://mail.python.org/mailman/listinfo/python-list
