Exercise 1

def find_dups(list):

""" (list) -> set
""" 
elem_set = set()
dups_set = set()
for entry in list:
    len_initial = len(elem_set)
    elem_set.add(entry)
    len_after = len(elem_set)
    if len_initial == len_after:
        dups_set.add(entry)
return(dups_set)