a = [10,20,30,20,10,50,60,40,80,50,40]  
  
dup_items = set()  
uniq_items = []  
for x in a:  
    if x not in dup_items:  
        uniq_items.append(x)  
        dup_items.add(x)  
  
print(dup_items) 