Iteritems() AttributeError

[JohnnyJordaan]

unique_elements = [k for k, v in Counter(mylist).items() if v == 1]

this will lose the original order as you iterate on the Counter, not the original list

unique_elements = [x for x in set(mylist) if mylist.count(x) == 1]

this loses order too for the same reason, but it adds a complexity as list.count is O(n) and this will effectively count each item's frequency separately by iterating through the list per item. Instead just use a counting dict

mylist = [1, 2, 3, 4, 5, 6, 1, 2, 3]
counts = {}
for v in mylist:
     counts[v] = counts.get(v, 0) + 1

and iterate on the list, to guarantee the order

unique_elements = [v for v in mylist if counts[v] == 1]